Complementary oligonucleotide probes specific for the human pro-opiomelanocortin (POMC) mRNA were used to analyze the expression of POMC gene in 56 human postmortem pituitaries by in situ hybridization histochemistry. POMC transcripts were visualized by autoradiography in anterior lobe of the pituitary where their distribution was in a 'patchy-like' pattern. No hybridization could be observed in the posterior lobe of the pituitary. We examined pituitaries from several controls and from patients dying with schizophrenia, Parkinson's disease. Alzheimer's disease, Wernicke's encephalopathy and depressive illness. Computer-assisted microdensitometric semiquantification of POMC mRNA using a complementary oligonucleotide as hybridization standard, revealed no statistically significant effect of postmortem delay (between 2.5 and 66 h), of gender, age (between 22 and 103) or cause of death in 56 human pituitary glands. A large variation in POMC levels was already observed among all 30 control cases. The levels of POMC mRNA observed in pituitaries from different pathologies did not show a significant variation when compared with control cases.