The susceptibility of microorganisms (Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, E. coli, Klebsiella pneumoniae, Salmonella spp. and Haemophilus influenzae) frequently occurring in outpatients (treated by practitioners) to six kinds of antibiotics [ampicillin (ABPC), cefazolin (CEZ), erythromycin (EM), minocycline (MNC), gentamicin (GM) and thiamphenicol (TP)] was determined by the standard method established by the Japan Society of Chemotherapy. 1) There were few multiple-antibiotic-resistant urine isolates from patients with a simple urinary tract infection, whereas urine isolates from patients with a complicated urinary tract infection contained many multiple-antibiotic resistant organisms. 2) Isolates from patients with a respiratory tract infection (sputum and tonsillar secretions isolates) and isolates from patients with acute purulent otitis media (purulent discharge isolates) contained few multiple-antibiotic-resistant organisms except for EM-resistant Streptococcus pyogenes. 3) Superficial pus isolates contained many multiple-antibiotic-resistant organisms, while bile isolates were relatively free from multiple-antibiotic resistant organisms. 4) When the results of the previous8,9) and present investigations were compared with the reports of other Japanese investigators1,5,6), suggestive evidence was provided that organisms resistant to macrolides and chloramphenicol showed a tendency to decrease, whereas organisms resistant to penicillins, cephalosporins and aminoglycoside antibiotics were on the increase.