Prolactin and alpha-1,4-glucosidase levels in seminal plasma were measured in poorly coagulated (I), deficiently coagulated (II) and normally coagulated (III and IV) human ejaculates having 0-20%, 21-50% and 51-100% coagulum respectively 4 min after emission. The prolactin concentration (ng ml-1, mean +/- SEM) in poorly coagulated (5.2 +/- 0.48) and deficiently coagulated (7.6 +/- 0.72) samples was significantly lower than in the normally coagulated groups III (51-75% coagulum, 8.2 +/- 0.43) and IV (76-100% coagulum, 9.9 +/- 0.59) as well as the presumably fertile samples (9.2 +/- 0.74). A highly significant positive correlation was observed between the prolactin level and the percentage coagulum of the ejaculates (r = 0.686, n = 58, P less than 0.001). In contrast, the epididymal marker, alpha-glucosidase showed no relationship to seminal coagulation.