Twenty-five patients were treated with ticarcillin disodium, 18 of whom had anaerobic infections that included pleuropulmonary infections (seven), mandibular osteomyelitis (four), perirectal abscess (two), sepsis, primary site unknown (one), liver abscess (one), pelvic abscess (one), decubitus ulcer (one), and synergistic gangrene (one). Seven had no anaerobic infections. Three had anaerobic septicemia. Culture results included anaerobes: peptococci (ten), peptostreptococci (ten), Bacteroides fragilis (six), Bacteroides not fragilis (ten), eubacteria (three), fusobacteria (two), Clostridium (one), Veillonella (one), and acidaminococcus (one); aerobes: Proteus (three), Klebsiella (two), Escherichia coli (two), and streptococci (two). Six patients with mixed aerobic infections initially received gentamicin sulfate in addition. The serum levels were 110 +/- 20 microgram/ml one hour after intravenous infusion of 5 g of ticarcillin disodium. All anaerobic isolates were susceptible at less than or equal to 100 microgram/ml and 85% by less than or equal to 25 microgram/ml of ticarcillin. Sixteen patients responded well to ticarcillin and two failed to respond. Our study suggests that ticarcillin is useful in the treatment of anaerobic infections.