Some mechanisms of inhibition by distamycin A of transduction of antibiotic resistance markers of R-factors (RI drd and R222) with the moderate phage PI kc in E. coli were studied. The kinetics of the transduction of the R-factor markers was investigated in comparison with the stages of interaction of PI kc phage particles with bacterial cells of E. coli K-12 carrying the R-factors such as RI and R222 -- phage PI kc -- E. coli C6000. Later the effect of distamycin A on transduction of the above R-factors was studied using the same system. It was shown that distamycin A in concentrations of 75 gamma/ml suppressed the transduction of the R-markers when added to the transduction mixture simultaneously with the phage. The transduction rate decreased 15 times if the drug was added 5 minutes after beginning of the phage contact with the recipient culture. Addition of distamycin A at the 20th minute of the experiment induced no inhibition of the transduction of the R-factor markers. Preliminary 18-hour exposure to distamycin A of the recipient culture and phagolysates possessing transduction capacity resulted in decreased rates of the transduction of the antibiotic resistance markers 35 to 40 times. No inhibitory effect of distamycin A on the process of phenotypic manifestation of the antibiotic resistance markers of the R-factors was noted. The experiments showed that distamycin A affected the early stages of interaction of the transducing particles with the recipient culture, possibly the process of penetration of the transducing DNA of the R-factors into the cells of the recipient culture.