Fifty rabbits, 44 cottontails (Sylvilagus floridanus) and six swamp rabbits (Sylvilagus aquaticus), were collected from the Mississippi Delta Area. Serum and tissue from these animals were studied for evidence of leptospirosis. Leptospira interrogans antibodies were demonstrated in 77% (37/48) of the serums collected, of which 21% (10/48) had significant titers. Serotypes most frequently encountered were ballum, australis, icterohaemorrhagiae, canicola, and grippotyphosa. Focal nephritis was observed histologically in 92% (46/50) of the kidneys. Isolation of grippotyphosa was made from 8% (4/50) of the kidneys collected. These studies have assisted in establishing the importance of cottontail and swamp rabbits as reservoirs for leptospires and have also identified two new host-serotype relationships.