The aim of the study was to evaluate 4-nitrophenylarsonic acid efficacy (Histostat® 50; Alpharma Trade Inc., USA) and metronidazol (Avimetronid; Polfa Grodzisk) in preventing turkeys histomoniasis. 10 turkeys with histomoniasis disorder and 10 healthy 10-week old turkeys' were divided into three groups (I, II, III). Turkeys from group I were the control group. The turkeys from groups II and III were administered Avimetronid at a dose of 2.5 g/kg and Histostat® 50 at a dose of 0.37 g/kg in their feed for 5 weeks, respectively. Clinical observations, anatomopathological examinations, parasitological examinations of cloacae swabs as well as hematological (RBC, WBC, leukogram) and biochemical examinations (ALT, AST, LDH) of the blood were carried out before the experiment and in the 5th week of its duration. The results indicated that 4-nitrophenylarsonic acid is highly effective in preventing histomoniasis and that metronidazol also has therapeutic proprieties. Although no side effects were noted in the turkeys receiving the examined 4-nitrophenylarsonic acid, it nevertheless seems that there is a danger of arsenic compounds cumulating in turkeys' organisms.