Nasal secretions from Papua New Guinea children were cultured using selective agents, to determine the prevalence of multiple colonization for both S. pneumoniae and H. influenzae. 29.5% of 156 and 53% of 93 carriage positive subjects harbored more than one type of S. pneumoniae and H. influenzae respectively. Of 95 strains of pneumococci isolated from multiply colonized children, 40% were relatively resistant to benzylpenicillin. In more than one half of the children in this group both penicillin sensitive and resistant serotypes coexisted. Significantly more penicillin resistant pneumococci were isolated from children with ready access to primary and regional health care services. Among H. influenzae the prevalence of multiple isolations due to nonencapsulated variants only, and encapsulated plus nonencapsulated organisms was similar. The commonest biotypes were types I, II, III and V, and each was similarly associated with multiple carriage.