In 18 males (age 49--79 yrs) without endocrine diseases, testosterone, free testosterone fraction, LH, FSH and cortisol (as indicator for stress) were determined in the early stage of an acute myocardia infarction. Blood was taken on admission as well as every 4 hours up to meanly 43 hours. The patients were separated in 2 groups for proving whether alterations of the parameters may depend on the severity of the myocardial infarction (group A=severe infarction; group B=not severe infarction). Testosterone showed a rapid decrease in the first 11 hours after admission, which continued less striking to the end of the investigation. Testosterone was significantly decreased in group A in comparison to group B. LH and FSH in both groups together were remarkably reduced during the whole time. Whereas group A demonstrated a tendency to decreased values in comparison to group B for LH, there were not any essential differences between the two groups for FSH. The free testosterone fraction was not altered. Cortisol in group A was twice as high as in group B during the entire investigation. The systolic pressure in group A was generally lower than in group B during the whole time. The results demonstrate an important reduction of the secretion of testosterone, LH and FSH during the early stage of the acute myocardial infarction. The testosterone suppression seems to be dependent on the severity of the myocardial infarction. These alterations may be caused by a general impaired perfusion as a consequence of myocardial infarction and a suppressive effect of increased cortisol values on testosterone levels.