Two diphenylantimony(III) derivatives of dithiophosphorus ligands, i.e. Ph2SbS2PPh2 and Ph2SbS2P(OPr-i)2, which were previously found to exhibit antitumor properties, have been now investigated for potential mutagenic effects in healthy and Ehrlich ascites tumor-bearing mice. Two short-term tests, i.e. the micronucleus test and the cytogenetic analysis, were used as end-points for mutagenicity. The results are consistent with a mutagenic potential for both organoantimony(III) compounds tested, the effect being higher for the phosphorodithioato derivative.