Effects of two water-soluble derivatives of fullerene C60-o-aminocaproic acid (C60-ACA) and C60 sodium salt of omega-aminocaproic acid (C60-Na-ACA) on in vitro cytomegalovirus (CMV) infection were studied. C60-Na-ACA 4-5-fold inhibited the cytopathic effect of CMV in comparison with C60-ACA, the effective dose for C60-Na-ACA being 0.6 microgram/ml and that for C60-ACA 2.7 micrograms/ml. Immunocytochemical analysis of virus proteins in infected cells has shown that C60-Na-ACA inhibits the production of late structural CMV protein gB, but does not modify the expression of immediate early nonstructural protein IEp72. Studies of cell viability, growth characteristics, and DNA synthesis revealed that the cytotoxic effect of C60-Na-ACA on human diploid fibroblasts in negligible, the cytotoxicity index varying from 160 to 1500 micrograms/ml in different tests. Selectivity index for C60-Na-ACA is 267-2500, which differs negligibly from that of gancyclovir (100-1000), while the cytotoxicity of C60-Na-ACA is essentially lower.