Sparfloxacin (SPFX), a new oral quinolone antimicrobial, was evaluated for the clinical efficacy against skin/soft tissue structural and osteomyelitic infections. SPFX was administered to a total of 101 patients with various infections such as infected atheroma, periproctal abscess, subcutaneous abscess, wound infections, felon, cellulitis, furuncle, pilonidal sinus, sappurative mastitis, lymphangitis, hemorrhoidal fistula, osteomyelitis. The clinical efficacy in the evaluable 101 cases was assessed by the physician in charge as excellent in 19 cases, good in 64, fair in 11 and poor in 7, the efficacy rate being 82.2%. In contrast, the clinical efficacy in 101 evaluable cases by the criteria of the committee as excellent in 36 cases, good in 45, fair in 8, and poor in 12, the efficacy rate being 80.2%. Clinical efficacy rating was not significantly difference between 200 mg/day group and 300 mg/day group. The bacteriological eradication rate was 86.5% in 53 cases with monomicrobial infection and 90.3% in 33 cases with polymicrobial infections. Of 18 cases whose infections were previously intractable with other drugs and treated thereafter with SPFX, 15 were judged in the efficacy as excellent or good. The side effects observed in 2 cases during the treatment were epigastralgia and nausea which were tolerable and did not require withdrawal of SPFX. No abnormal laboratory value was found in the several required tests. The MIC values measured for 108 strains (90.0%) of 120 clinical isolated of 35 species were lower than 0.78 microgram/ml.