The current sensitivity of enterococci to a total of 20 antibiotics (5 penicillins, 11 cephalosporins, cotrimoxazole (trimethoprim + sulfamethoxazole), nitrofurantoin, tetracycline, and doxycycline) was evaluated by determining the respective MICs. Ampicillin is certainly the drug of first choice for the treatment of moderately severe infections due to enterococci. Nitrofurantoin is equally effective in urinary tract infections. Co-trimoxazole is a suitable alternative in the presence of penicillin allergy. Penicillin G and tetracyclines should not be used in enterococcal infections. All cephalosporins presently available are ineffective against these bacteria. In view of the results of in vitro sensitivity test for bacteria, acylureido penicillins should be preferred to cephalosporins in very serious infections and mixed infections, especially in immunocompromised hosts. Azlocillin, mezlocillin and piperacillin are the most effective drugs to prevent superinfections with enterococci in clinically and bacteriologically defined situations. The combination of these drugs with aminoglycosides is the most effective antibiotic therapy for serious infections known so far. The influence of inoculum density on MIC and MBC values was investigated. The detailed discussion of the laboratory's own results and of the data reported in the literature points to the inadequacies of the test methods which have been used so far.