The objective of the study was to determine the ceftriaxone levels achievable within lesions (toe or forefoot area) in patients with septic gangrene and to investigate the relationship between macro- and microcirculatory parameters and antibiotic concentration. Fifteen patients with severe chronic peripheral occlusive disease received an intravenous injection of 2 g of ceftriaxone. Antibiotic levels in venous and capillary blood and in an exudative part of the lesion were measured. Macrocirculatory functions were assessed by Doppler sonography, plethysmography, and angiography; microcirculatory functions were assessed by quantitative capillaroscopy and fluorescence video microscopy. The mean antibiotic concentrations measured between 4 and 8 h after injection were 92 +/- 26 micrograms/ml in venous blood and 84 +/- 46 micrograms/ml in capillary blood. The concentration in tissue reached its maximum 4 h after injection; the average concentration at between 2 and 8 h was 95 +/- 55 micrograms/ml. Only dynamic capillary parameters showed significant (P < 0.01) correlations to antibiotic levels in tissue. Significantly (P < 0.01) higher levels in tissue were observed in patients with adequate microcirculatory functions (138 +/- 48 micrograms/ml) than in patients with poor microcirculatory function (51 +/- 26 micrograms/ml). Microcirculatory dysfunction appears to be the limiting factor for tissue antibiotic levels. However, even those patients with poor microcirculatory function showed tissue antibiotic levels that were above the MICs for the pathogens most frequently isolated from gangrenous lesions. Therefore, intravenous application was found to be adequate and additional measures such as intra-arterial therapy or Bier's occlusion are basically unnecessary. Our finding that microcirculatory function is the limiting factor for the tissue antibiotic concentration is corroborated by computations based on a three-compartment model.