The aim of the experiments was to evaluate the effect of administration of cysteine, methionine, thiocystine, and thiosulphate upon the activity of mercaptopyruvate sulphurtransferase (MPST) and rhodanese in mouse liver. It was found that rhodanese activity increased following thiocystine and methionine administration and showed a smaller increase after cysteine and thiosulphate. The MPST activity significantly increased after cysteine and to a lesser extent after thiocystine and thiosulphate. On the other hand, methionine seemed to exert no effect upon the enzymatic activity. The results suggested that methionine metabolic cycle in mouse liver proceeded from cysteine to sulphane sulphur as thiocystine and, therefore, these three compounds increased rhodanese activity. Thiosulphate seemed rather to be involved in metabolic changes related to maintaining the stability of the physiological thiosulphate level and activated both the enzymes.