From January through June 1980 seven colleges and universities in various parts of New York State (NYS) reported outbreaks of conjunctivitis affecting at least 1,500 students of both sexes. Of the 125 conjunctival swabs tested in our laboratory, organisms identified as nontypable Streptococcus pneumoniae were isolated in pure culture from 24% and in combination with other organisms from 22%. Although bile-soluble and susceptible to optochin, the isolates had a dry-colony appearance and no typable capsule with the Neufeld capsular-swelling test. Mouse passage of four representative NYS isolates did not stimulate production of a typable capsule. We subsequently chose to refer to these isolates as S. pneumoniae-like organisms. Of primary importance to our study, all NYS isolates tested were similar in biochemical and immunological reactions, antibiotic susceptibility, and virulence in mice. Of 18 strains referred to us from three other outbreaks (California, 1980; NYS, 1981; Illinois, 1981), four of the six tested biochemically gave the same biochemical reactions as the four NYS isolates, and 16 of the 18 tested immunologically reacted strongly with antisera produced against those four isolates, showing line(s) of identity with each other and with the NYS isolates.