The paper presents the cycle of margarine production with special attention to the process of hardening of vegetable oils using nickel formate as catalyst. Test examination (patch tests) was carried out with standard set and nickel formate in 10 workers of hardening department and 24 female workers of packing room. In 2 workers contact dermatitis caused by sensitization to nio nickel formate was observed. In 5 workers was found latent allergy to nickel and in 12 female workers latent allergy to chromium and nickel. In the control group containing intellectual workers, uniform in regard to sex and age, the results of patch tests were negative.