A total of 33 clinical isolates of Capnocytophaga spp. were susceptible to 4-quinolone antimicrobial agents. The antipseudomonal penicillins tested were equally active against all isolates, as were cefuroxime, ceftriaxone, ceftizoxime, cefotaxime, latamoxef, and ceftazidime. Most isolates were resistant to trimethoprim, and some were resistant to aztreonam. Most regimens for the empirical treatment of septic episodes in immunocompromised patients are suitable for the treatment of Capnocytophaga spp. infections.