A total of 5348 isolates of Streptococcus pneumoniae was serotyped and screened for insusceptibility to tetracycline, penicillin, erythromycin and chloramphenicol. Of these, 4238 (79%) were isolated from patients who had pneumonia or meningitis or were bacteraemic. Altogether, 3948 (74%) of the isolates belonged to one or other of the serotypes 1, 3, 4, 6, 8, 9, 14, 19 or 23 with serotypes 6, 14, 18, 19 and 23 being frequent causes of invasive disease in young children. Many isolates of type 1 were isolated from pneumonia and few from meningitis. Some 768 (14%) isolates were insusceptible to one or more antibiotic and 591 of these belonged to serotypes 6, 9, 14, 19 or 23. Representatives of type 14 resistant to erythromycin were prominent from 1986 onwards. There was an increase in the number of multi-resistant pneumococci from 1985. Among these were isolates of type 23 insusceptible to penicillin, chloramphenicol and tetracycline and cultures of type 6 resistant additionally to erythromycin.