In a group of 600 patients treated in the Metropolitan Dermatological Hospital in Warsaw bacteriological examination were carried out of swabs from the untreated crural ulcers. In 95% of these cultures growth of pathological aerobic organisms was obtained. Coagulase-positive staphylococci (St. aureus) and Gram-negative bacteria (Pseudomonas aeruginosa, Proteus vulgaris, Enterobacter sp and E. coli) prevailed. In 27% of cases the cultured strains were resistant to the generally available antibiotics. In the second group in 70 patients no growth of anaerobes exclusively was noted. Pathological aerobes and anaerobes in the same case were found in 45% of cultures. In the remaining ones pathogenic aerobes were present with a similar frequency as in the preceding group. Of the anaerobes the most frequently cultured species were Gram-negative bacteria such as Bacteroides melaninogenicus, Bacteroides sp, and Bacteroides fragilis. Among pathogenic anerobic cocci Peptostreptococcus and Peptococcus were most frequent. In 2 cases spore-forming anaerobic bacteria (Clostridium perfringens) were obtained. Forty-eight percent of anaerobes were resistant to the commonly used antibiotics.