The combined action of polyene macrolide antibiotic amphotericin B and styryl dye RH 421 in model lipid membranes and in yeast Saccharomyces cerevisiae has been studied. RH 421 insertion inti the ergosterol-containing lipid bilayers led to the increase of the steady-state number of open amphotericin channels by 8.5 +/- 3.2 times. Paper disk agar diffusion method has demonstrated that RH 421 enhanced the antimicrobial effect of amphotericin B leading to an increase in the zone of growth inhibition of S. cerevisiae strain by 1.5 times. Our data suggest that RH 421 is a potential synergist of amphotericin B and can be used in new formulations with improved pharmacological properties.