In a serological examination of 710 serum samples collected from human volunteers in Plateau State, Nigeria, 128 (18.0pc) had leptospiral antibody titres of 1:100 and above. The prevalence of antibodies to individual serovars were: hardjo 28 (21.9pc), pomona 18 (14.1pc), canicola 17 (13.3pc), grippotyphosa 15 (11.7pc), pyrogenes 13 (10.2pc), icterohaemorrhagiae 12 (0.4pc) and autumnalis 8 (6.3pc). There was no statistical difference in the prevalence rate of leptospirosis in the different local government areas (p greater than 0.05; X2). Among the occupational groups examined, the abattoir workers were particularly at risk with a prevalence rate of 29.5pc. A leptospiral variant of strain Hardjoprajitno was also isolated from the midstream urine of an abattoir worker who was apparently healthy. The isolation of Leptospira interrogans serovar hardjo in man is the first such report in Nigeria.