A nationwide survey of the prevalence of antimicrobial resistance among Streptococcus pneumoniae isolates from the middle ear fluid of children with acute otitis media (639 strains) and from throat-swab samples of healthy children (149 strains) was conducted in Finland during 1987-1990. The MICs of penicillin, cephalothin, cefaclor, erythromycin, trimethoprim, and co-trimoxazole were determined by the agar dilution method. Low-level resistance to penicillin (MIC, 0.1-1 microgram/mL) was found in 1.7% of the otitis-related and 1.3% of the healthy-carrier strains. No highly penicillin-resistant strains (MIC, > or = 2 micrograms/mL) were found. Six multiresistant strains were detected, three of them possibly belonging to a previously identified clone present in Finland since 1985. Eighty-five percent of the resistant otitis-related strains, including 9 of the 11 moderately penicillin-resistant strains (4 of which were multiresistant), belonged to the three most common serogroups (6, 19, and 23).