In a recent paper, Chesson (Environ. Entomol. 11: 531–537, 1982) proposed a model based on the binomial distribution which, when applied to field measurements of host mortality, can be used to obtain post hoc estimates of the probability of encounter of host-containing patches, and the conditional probability of parasitism (given encounter) for hosts present in such patches. Chesson recommends that these estimates be used to draw inferences concerning the behavior of searching parasitoids-in particular, to determine whether individuals of a given parasitoid species respond to between-patch variations in host density during search. Here, we examine the model and suggest that it may produce misleading behavioral conclusions if interpreted in the way its author recommends. Chesson's critique of an earlier study by Morrison, Lewis, and Nordlund (Environ. Entomol. 9:79–85, 1980) is also discussed.