The occurrence of penicillin resistance in clinical isolates of pneumococci was investigated in two clinical microbiological laboratories in Copenhagen, Denmark. One of the laboratories predominantly received samples from patients with frequent use of antibiotics mainly because of chronic lung diseases. In this laboratory, 6.3% of 245 isolates of pneumococci had intermediate resistance to penicillin. In the other laboratory, which received samples from a number of hospitals and general practice, only 1.3% of isolates of pneumococci had reduced sensitivity to penicillin. Penicillin-resistant pneumococci are rare in Denmark, but are more prevalent in patients who frequently use antibiotics.