The functional response of the fish predator Brachydanio rerio to changes in the density of 2 prey spp., Daphnia magna and the cercarial stage of the ectoparasitic digenean Transversotrema patialense is of the type II form where the instantaneous predation rate is unaffected by changes in prey density. A model is developed to describe this functional response, based on the concept of predator satiation. The number of prey items required to create satiation is dependent on the experimental procedures used to elicit the functional response. The fish predator, B. rerio, acts in the dual role of predator/host for the cercarial stage of T. patialense. The concomitant predation and infection processes created by this ecological association are characterized by constant instantaneous predation and infection rates which appear to be unaffected by changes in prey/parasite density. The infection process is unaffected by density dependent constraints over a wide range of exposure densities and the number of parasites attached per host is directly proportional to cercarial numbers. Stochastic elements are important determinants in the dynamics of the infection process and overdispersion in the frequency distribution of the number of parasites attached per host may be generated by heterogeneity between fish and heterogeneity in time created by changes in infective stage density. The relevance of concomitant predation and infection processes to the dynamics of digenean life cycles is discussed.