To investigate the acute and chronic effects in young men of exposure to chemical warfare containing mustards, the time course of changes in serum concentrations of total and free testosterone, dehydroepiandrosterone (DS), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and prolactin was evaluated in 16 men in the first three months and testicular function in 42 men one to three years after injury. Serum total and free testosterone and DS were markedly decreased in the first five weeks after exposure. The lowest values were: total testosterone 237 +/- 165, free testosterone 22.5 +/- 9.7, DS 39 +/- 25; as compared to controls: total testosterone 773 +/- 245 ng/dl, free testosterone 35.5 +/- 11.2 pg/ml and DS 207 +/- 37 micrograms/dl. FSH, LH, prolactin and 17 alpha-OH progesterone were normal in the first week. The response to GnRH was subnormal in four of five subjects. LH increased by the third and FSH and prolactin by the fifth week. All hormone levels had returned to normal by twelfth week after exposure. In 28 of 42 men seen one to three years following injury, sperm count was below 30 million cells/ml, and FSH was increased as compared to men with sperm above 60 million cells/ml. Testicular biopsy showed complete or relative arrest of spermatogenesis. This study demonstrates that the exposure to sulphur mustard results in very low androgen levels and hypo-responsiveness to GnRH in the first five weeks and normalization by the twelfth week after injury. However, side effects of mustard on sperm cells persist and may cause defective spermatogenesis years after exposure.