Seventy-nine strains of legionella spp. and 13 non-legionella isolates were tested using a commercial latex agglutination kit. Cross-reactions were observed for all strains of Legionella pneumophila serogroup 12 examined between latex particles coated with rabbit antibodies raised against L. pneumophila serogroup 1 and those coated with rabbit antibodies to serogroups 2-14. Strains of L. pneumophila serogroup 1 did not cross-react with latex particles directed against L. pneumophila serogroups 2-14. This suggests that L. pneumophila serogroup 12 shares common surface antigens with L. pneumophila serogroup 1, and that conversely serogroup 1 isolates do not share major surface antigen determinants with serogroups 2-14. All other isolates tested gave expected results.