A generalized competition model for predators or parasites was developedfrom data obtained from a specific parasite–host system. It was structuredin three parts. The first simulates the effects of exploitation, where thenumber of attacks and their distribution among prey or hosts determine howmany prey or hosts survive. Since the negative binomial distributiondescribed these distributions consistently, the exploitation submodel wasdeveloped from it. The second portion of the competition model concernedinterference between searching predators and parasites. Althoughinterference is a universal phenomenon, we were able to show that itseffects become important only at predator densities much higher than thosethat occur in nature. Thus the interference component can be essentiallyignored. The third and final component concerned the outcome of competitionbetween parasite progeny within their host. It was developed from Fujii’scompetition model which allows for the simulation of both scramble andcontest types of competition.These three submodels of competition werecombined and coupled with a previously published model of the effects ofprey density on attack. In this way the full consequences of different preyand predator densities could be simulated using a model whose constituentparts had been carefully tested for descriptive adequacy. The simulationsshowed the way individual predator attack, per cent predation, and progenyproduction were affected by different degrees of contagion in thedistribution of attacks, by scramble vs. contest competition, and by thedegree to which parasites could avoid hosts already attacked.