The chapters that follow a review of the literature, describe firstly the serological and culture techniques which were used to study leptospiral infection in pigs, and secondly an attempt to define the epidemiology of leptospirosis in pigs in New Zealand. After this an investigation of cell mediated immunity in pigs which had been infected with serovar pomona is described. During the study a number of experiments were conducted with the aim of defining the optimal conditions of cell culture for these transformation experiments, and a number of these have been reported in the appendices.