The great variability of the effects of topically applied antibiotic and chemotherapeutic drugs to the central nervous system is not generally appreciated, in spite of numerous clinical and experimental studies. Many of these drugs are epileptogenic. Others are severe cortical "depressants," and still others have no significant effect on the electrical activity or histological appearance of the central nervous system. To keep up with the rapid development of new antibacterial agents, Hanbery and Ajmone-Marsan1in 1954 investigated the effects on the central nervous system of chloramphenicol, penicillin, streptomycin, bacitracin, neomycin, erythromycin, chlortetracycline (Aureomycin), oxytetracycline (Terramycin), and polymyxin B. Before this, Russell and Falconer,2Jasper et al,3and Botterell et al4investigated the effects of various sulfonamides on the brain; Walker et al5,6investigated the effects of penicillin on the cortex; and Teng et al7,8studied bacitracin. Newer drugs are coming on the market all