The experiment was carried out on 300 one-day-old Big-6 turkey-hens which for sixteen weeks administrated 1,2,4-triasole derivative [3-(2-pyridyl)-4-phenyl-1,2,4-triasole-5-carboxylic acid] as additive to drinking water. The aim of the present study was to estimate the influence of the tested compound on some parameters of blood and effectiveness of rearing of turkey-hens. After 5, 9, 13 and 16 weeks blood was taken from 60 turkey-hens (from each group) in order to carry out hematological, immunological and biochemical examinations of the blood. An essentially lower content of total protein, glucose and increased AST and ALT activity, percentage of phagocyting cells and NBT were noticed in the blood revealing the possibility in turkey-hens which received 1,2,4-triasole additive. The body weight of the group with 1,2,4-triasole derivative was higher compared to the weight of the control. The fed conversion ratio was higher in this group as compared to control group. The survivability of the experimental groups was better than in the control.