Hi Laura
This text is going to be quite long so i´d better start it now. :p
There are lots of episodes in which he appears but let me try to help you with this. :rolleyes: Star Labs was mentioned since the very first episodes of the series but I vividly remember it in "Pheromone My Lovely"..
the first episode ever that i remember seeing Dr Klein was in "Don´t Tug on Superman´s Cape" in which he appears dizzy and tells superman that someone stole the kryptonite he was keeping for a treatment. :p
He appears again in "Ultra Woman" where he helps Superman get back his superpowers by fixing a videocamera that the Newtchrit sisters invented using red Kryptonite to transfer his powers to the older sister.
On the next week he appeared again doing a DNA test to prove superman didn´t have a son with another woman in "A Chip off the Old Clark". He also appeared at the end of the episode to tell them that the boy was losinh his superpowers.
wow. on the next week he also had an appearance but in "Super Mann" the episode about the Nazi revolution in Metropolis. (i don´t remember it very well and soon I´ll give you some FDK about it)
in the episode " Home is Where hurt is" he doesn´t appear but he talks to Lois over the phone and Superman authorize him to give Lois a piece of kryptonite to help him with an infection he got from a virus Mindy Churchil used against him.
He comes back to scene in "Seconds" where he appears taking care of Lois´ clone.
He also appears in Oedipus Wreck (unfortunately i don´t have this episode anymore but i guess he helped Clark with information about the appliance Herkimer Johnson, Bad Brain´s brother, invented and that helped Lois get back her memories).
He appears in " It´s a Small World Afterall"
(this episode didn´t come in Brazil so i never really saw it... i hope one day i can.. but i guess he helps Clark get to his normal height cause i think he or Superman got shrunk on this episode.
He also appears in "Through A Glass, Darkly" where he is working on a device with lasers which Superman borrows to save Perry, Jimmy and the rest od the city from a bomb which was armed by Sarah and Ching to test the Man of Steel.
Now at the 4th season...
I dont remember him appearing on this sequel but i think in "Battleground Earth" he called Lois to tell her the kryptonite was stolen. Later on, they find out that the government itself stole it to prevent the kryptonians to command Earth.
he also appeared in the episode in "Brutal Youth" where he helped L&C help Jimmy Olsen as well as he told Lois about Superman regenerating cells that stablish and reduce the process of aging.
wow... almost finished..
He appears again in "Dead Lois Walking" where Lois and he himself were targets of an angry revenge-seeking scientist. This was the episode you were talking to where we finally get to see him working in administration after a guy there quit. I think he was like a human resources manager cause he was talking about vacation schedules... anyway, in this episode,Lois was accused of murder and he helped Superman with the bullet system as long as Superman could bring his much younger though brillant doctor girlfriend to help him there and she actually did figure something out.
he appears again at "Bob & Carol, Lois & CLark" where he explains about magnatism and how Superman should avoid another encounter with DeathStroke.
He also appears in "Lethal Weapon" where he helps Superman deals with his superpowers which are out of control.
:p
He made one of his appearances in "Shadow of a Doubt" in which he tried helping superman find out how a mysterioys shadow-man was working.
"Voice From The Past" is an episode in which he also appeared but i just couldn´t find my tape here so i cant tell you much about this episode by memory.
Finalllllllyyyyyy the last episode in which he appears was "Toy Story" where he helps Superman and Lois find out about a transmittor that is used to kidnap children using toys to do so...
phewwwwwww... quite a busy job gathering all this information.. i hope i´ve helped...
i cant believe i forgot such an important thing... about the Nazi thing... Superman was hit by an atomic explosion and he was radioactive for 30.000. He got rid of the problem going to the sun and using its gravity to clean himself up.