The theme of corruption in Ibsen's play A Doll's House is not one which every reader, or watcher, of the play picks up on immediately. It can be a very hidden and difficult idea for some.
The corruption in the play exists within three different characters: Nora, Dr. Rank, and Nils Krogstad.
Nora's corruption is seen in her morally condemnable act of signing her father's name to the loan documents. Nora, after the fact, believes that her actions are ones which will pass down to her children, making them genetic.
Dr. Rank's corruption is seen in his inherited disease (tuberculosis). He believes that the disease was passed down by his father who lived a very corrupt and reprehensible life. Again, this points to the idea that corruption can be passed down through genetics.
Last, but not least, Nils Krogstad's attempt to blackmail Nora with his knowledge of her fraudulent loan, in order to keep his job, shows his own corrupt nature.