Patients with cancer and suspected sepsis were treated in a prospective, randomized trial with 1 of 4 cephalosporin-aminoglycoside combinations: cephalothin and tobramycin; cephalothin and gentamicin; cefamandole and tobramycin; or cefamandole and gentamicin. Carbenicillin was added if the absolute granulocyte count was < 1000/mm3. Of 199 patients receiving 20 or more doses of an aminoglycoside and having serial determination of serum creatinines, nephrotoxicity developed in 7 (3.5%) given any of the 4 combinations. There were no significant differences between patients receiving either cephalosporin or aminoglycoside. Nephrotoxicity developed less frequently among children (2 of 125; 1.6%) than adults (5 of 74; 6.8%).