The effects of amitraz, a formamidine pesticide, were investigated in four-week old outbred male Wistar rats on certain classic toxicological and haematological parameters as well as on specific immune functions. The animals were treated, per os by gavage for 28 days, in a five-day treatment two days break system, with 26.5, 21.1, 10.6 and 5.29 mg/kg/day amitraz. On the 29th day, organ weights of the thymus, heart, lung, spleen, liver, kidneys, adrenals, testicles and popliteal lymph node; WBC and RBC counts, Ht, MCV, haemoglobin; and cell content of the femoral bone marrow were determined. In two separate groups, the effects of amitraz on the PFC content of the spleen, and on the maximum level and time course of DTH reaction, were investigated. Amitraz in 26.5 mg/kg dose increased relative adrenal weight, and decreased relative liver weight, MCV value, PFC content of the spleen, and the maximum level of DTH reaction. The 21.1 mg/kg dose decreased only MCV value, while 10.6 mg/kg elevated the liver-to-brain weight ratio. Based of these findings, a NOEL dose of 5.29 mg/kg was determined for amitraz in this experimental system; while the LOEL doses were 10.6 mg/kg for the general toxicological, 21.1 mg/kg for the haematological and 26.5 mg/kg for the immune function parameters. The results show that the exposure sensitivity of these immune functions to amitraz is lower than that of some other toxicological and haematological parameters.