OBJECTIVE: To investigate the potential source of a case of Legionnaires' disease caused by an unusual serotype of Legionella pneumophila serogroup 1 (Lp1) in regional Victoria in May 2001. METHOD: Epidemiological and environmental investigation of the source of infection of a case of Legionnaires' disease in regional Victoria in May 2001. RESULTS: Extensive environmental investigations did not reveal any cooling water tower systems close to the residence or the shopping centre that the case visited prior to illness. The sputum culture and a soil sample from the field at the plant nursery where the case worked prior to illness were both positive for Legionella pneumophilia serogroup 1, MDU pulsovar 97:103. CONCLUSION: Legionella pneumophila has been found in soil and was further found to be associated with a case of Legionella pneumophila. IMPLICATIONS: Public health authorities should consider exposures to soil and potting mixes when investigating cases of Legionella pneumophila where the case has no apparent association with cooling towers. Safe gardening practices should be promoted among the community.