The aim 'of this investigation was to determine the concentrations of triiodothyronine (T3), thyroxine (T4) and cortisol in blood plasma from calves during the first 32 h of postnatal life, as well as at 7 days old. The experiment involved two groups of calves. The first group was offered the standard amount of colostrum while the second group received half the recommended amount. The results obtained showed that the calves were born with high plasma concentrations of 73, 74 and cortisol up to four times greater than values found at 7 days old. In the calves given the full ration of colostrum there was a gradual increase of mean 73 concentration to levels which plateaued from 8 to 28 h after birth, while the level of T4 increased slightly but significantly up to 18 h. Sharp highly significant increases in 73 and 74 concentrations were observed during the first 4 h of postnatal life in the group of calves given half the usual amount of colostrum to levels which persisted up to 20 h. Except at 4 and 20 h there were no significant differences between the groups. At 7 days old the levels of plasma 73 and 74 in both groups of calves were within the limits found for adult animals. The plasma concentrations of cortisol decreased during the first 18 h afterbirth in both groups of calves and then increased somewhat. At 32 h the mean concentration was higher in group two than in group one. At 7 days old cortisol concentrations were up to four times lower than the level immediately after birth. It was concluded that a decrease in the amount of colostrum consumed had only minor effects on the plasma concentrations of the examined hormones in neonatal calves.