Cytogenetic analysis of Muntiacus muntjac fibroblast cells exposed to the xanthene dye, Rhodamine B, revealed a significant increase in chromosomal aberrations. The M. muntjac fibroblasts were exposed to various concentrations of Rhodamine B and examined for increases in aberration frequencies. As the concentration of Rhodamine B was increased there was an increase in the percentage and types of aberrations observed up to 20 micrograms/ml concentrations. At the 20 micrograms/ml exposure levels, there was a decrease in the total aberration frequencies and an increase in the types of aberrations observed; these results may be related to toxicity at the higher concentration. These results suggest the need for further study of the effects of Rhodamine B in vitro and in vivo.