Three cases of infection, including two fatal ones, caused by pneumococci relatively resistant to penicillin are reported. The patients were a 19-year-old New Guinean with fatal multisegmental pneumonia, a 10-week-old Caucasian infant who died suddenly from purulent meningitis, and an Australian Aboriginal child aged two years with bronchiectasis complicated by pneumococcal bacteraemia. The pneumococci isolated (serotypes 6, 16 and 19) showed minimal inhibitory concentrations of penicillin G ranging from 0-1 microgram/ml to 1-0 microgram/ml (resistance ratios five to 50) and were also relatively resistant to penicillin V, methicillin, cloxacillin and cephalosporins.