We report a retrospective account of 200 patients who have been surveyed after having undergone neurosurgical intervention. They received as perioperative antibiotic prophylaxis a combination of Mezlocillin and Oxacillin in a ratio of 2:1 (Optocillin) in their management. The clinical and bacteriological efficacy including the side effects was examined with standardisation of sterility measures in the operating theatre, careful standardised operative procedures and ward after care. No problems in wound healing were found. There was no certain evidence of side effects.