Eight hundred and fifty-two (852) blood sera were drawn in 1980 and 1981 from populations residing in 30 agricultural settlements (having a total population of 16,240). These sera were tested for the presence of antibodies against 15 different antigens of Legionella species (L. pneumophila serogroups 1-8 and seven other Legionella, i.e. bozemanii, gormanii, micdadei, jordanis, dumoffi, longbeacheue and oakridgensis). The results indicate a significant (P less than 0.02) excess in the percentage of sera positive for L. pneumophila (serogroups 1-8) among sewage and non-sewage irrigation and fish pond workers as compared to the control group (4.5% vs 1.5%). For the other Legionella species, there was no difference among the above groups.