The quantitative and qualitative bacteriological investigations of 63 patients were done on ischaemic ulcerations before reconstructive vascular surgery and at 7 day intervals after the operation. Among the isolated bacteria the most common were Gram positive (62.9%), especially Staphylococcus aureus. Amputations due to non-healing ulcers were performed on 8 patients, who had ankle brachial index (ABI) lower than 0.47. In 55 patients with ABI higher than 0.47 (with the exception of one case) free skin grafts were applied to reduce the time of the ulcers healing. Primary healing of ulcers covered with free-skin grafts was achieved in 44 out of 55 patients (80%). In 11 patients, were free-skin grafts had failed, ulcerations were healed following the repetition of the free-skin grafts. The healing results of skin grafts statistically were significantly better in the group where the number of bacteria in 1 cm2 of ulceration was lower than 50.000. The severity of infections in ulcers makes the healing process of skin grafts impossible. Quantitative bacteriology additionally helps in objective evaluation of granulating tissue and facilitates choice of proper skin grafting time. This study has shown the usefulness of quantitative bacteriology for the determination of the severity of infections in ulcers.