Strains of Streptococcus pneumoniae (N = 915) from clinical specimens were examined for penicillin resistance over a 2-year period. The prevalence of resistance [minimum inhibitory concentration (MIC) greater than 0.1 mg l-1] increased from 1.4 to 2.5% per year during this time. In addition, 83% of penicillin-resistant pneumococci (PRP) showed resistance to chloramphenicol. Most PRP were isolated from uninfected children colonized with the organism, but two out of the three adult cases were clinically infected, one by cross-infection between in-patients. In only two cases was there an association with foreign travel. Three children showed prolonged carriage providing a potential reservoir of infection for other members of the community. The percentage of strains showing high level resistance (MIC greater than 1 mg l-1) increased from 0.7% to 1.9% of all isolates during the 2-year study period. This high prevalence of high level resistance has not been reported previously in the UK and if the trend continues, it will have serious implications for the management of invasive pneumococcal infection, particularly meningitis.