Several questions raised by the use of closed antibiotic-detergent irrigation in the treatment of chronic osteomyelitis were investigated by in vitro experiments. Although detergents are strongly alkaline and probably cause some inactivation of penicillin, methicillin, and oxacillin when mixed with them in irrigating solutions, the extent of this inactivation was not of sufficient magnitude to greatly reduce the in vitro effectivensess of these antibiotics against Staphylococcus aureus. Studies of penicillin-Alevaire combinations revealed no synergism of these two compounds against strains of penicillinase-producing Staphylococcus aureus; and, in fact these drugs did not inhibit the growth of such strains significantly.