Bacterial samples were obtained from the facial and forearm skin of atopic dermatitis (AD) patients and healthy subjects in humid summer weather. Staphylococcus (Staph) species bacteria were selectively sampled by a plate-contact technique using mannitol salt medium-coated film. Staph species were isolated from the film after the number of colonies was counted, and the species were determined by the API-Staph system and coagulase test. Large numbers of S. aureus were isolated in the samples from the facial skin of patients with severe dermatitis, as previously reported. The number of S. aureus colonies in the samples from the forearm skin of the patients was significantly greater than from the healthy subjects; the mean and standard deviation of colony forming units per 10 cm2, expressed as log10 value, were 1.64 +/- 0.96 for patients and 0.02 +/- 0.07 for healthy subjects (p < 0.01). One hundred and seventeen strains were isolated, and their sensitivities to ten antibiotics were tested. Ten of the strains were resistant to some antibiotics; all of these were isolated from patients. Penicillin type antibiotics had weak effects, but cephem type had strong effects. The number of S. aureus colonies isolated in this study was compared with the number isolated during the winter, in our previous study, in order to identify seasonal variations. The only significant seasonal difference was on the forearm skin of the AD patients, which had significantly more S. aureus colonies (p < 0.01) in this study. There were no significant seasonal differences in S. aureus numbers on the facial skin of patients or healthy subjects.