I should know this but...

What was the episode where Dr. Klein tells Clark that Superman is "not compatible" with a human woman?

Clark asks Bernie to do the research in Shadow of a Doubt, but they don't get the results until The Family Hour -- the final episode of the series.

Joy,
Lynn

Do you remember why Clark asks Bernie to do the research? Was there some specific reason? Was that the episode where Lois freaks out about the nursery school reservation list?

Clark askes Dr. Klein to do the tests after he and Lois have unprotected sex at the beginning of "Faster Than a Speeding Vixen" - after Lois "attacks" Clark in the kitchen.

In their conversation, Clark mentions that he's not sure if he *can* make babies and Lois suggests that he talk to Dr. Klein.

The episode with the nursery school list was the third season episode "The Dad Who Came In From The Cold." I don't know that either Lois or Clark freaked out about it, but it was definitely Clark who was worried that he wouldn't be a good dad on that episode, comparing himself to Jack Olsen and thinking his Superman duties would mean his kids hardly knew him.