Six Kenana calves between 2 and 4 months old were divided into two groups. Calves in group 1, were orally given DL-tryptophan in doses of 0.5g/kg, body weight during the 1^st week, 0.6g/kg, body weight during the 2^nd week, 0.7g/kg, body weight during the 3^rd week, and 1g/kg during the 4^th week. Calves in group2, were dosed with L-tryptophan in the same maner as described for group 1 calves. It has been shown that  DL-tryptophan or L-tryptophan given to young Kenana calves in single or repeated doses produced a very mild pulmonary lesion. The activity of 5-NT, SD and GD and concentration of urea in plasma of calves in both groups showed no change after dosing with tryptophan. Whereas the activity of GGT in plasma of all calves showed progressive increase after dosing.