Twenty-four h changes in plasma concentrations of Cortisol, prolactin and androgens in both sexes of primitive Asiatic pigs (Vietnamese - Sus scrofa vittatus) were investigated. Blood samples were drawn from indwelling femoral artery catheters and plasma concentrations of hormones were analysed by radioimmunoassay. All three investigated hormones showed statistically significant 24 h changes in boars with higher levels in the morning (cortisol, prolactin, and androgens) and in the early (prolactin) or late (cortisol) evening. Patterns of plasma cortisol and prolactin concentrations in gilts were the same as in boars, whereas androgen concentrations in gilts were not changed. The boars' androgens showed 24 h changes but without a consistent circadian rhythm. Only plasma cortisol concentrations in boars as well as in gilts had a circadian rhythm with the following cosine curve characteristics for boars and gilts, respectively: acrophases (point of 24 h with maximal hormone value) 9.24±5.23 h, 7.37±3.06 h; amplitudes 1.70±1.07, 2.25±1.67 ng/ml and 24 h means 9.20±0.72 and 7.05±0.68 ng/ml.