The effects of food availability and the presence of the entomopathogenic digenean parasite Plagiorchis elegans (Rudolphi) on the probability of Aedes aegypti (L.) preimagos to transform from one developmental stage to the next over consecutive 24- or 48-h periods were quantified. Under conditions of low food availability, 24- and 48-h transition probabilities for all larval instars to the next were reduced. Increases in food availability reversed this process, causing significant decreases in same-stage transition probabilities. However, as transition to successive stages increased among first, second, third, and fourth instars, there was a concomitant, significant increase in first- and fourth-instar mortality. Exposure to P. elegans cercariae caused significant decreases in the 24- and 48-h same-state probabilities for all preimago stages. Successive stage transitions for first, second, and third instars were significantly increased, whereas those of fourth instars and pupae were significantly decreased with exposure to parasites. Mortality among all preimago stages increased significantly with exposure, but was highest among fourth instars and pupae. There were strong food-by-parasite interaction effects among first, second, and third instars. Differences in transition probabilities increased with increasing food levels between control and parasite-exposed sets. Whereas there was no significant interaction effect between food and the presence of the parasite in pupae, significantly more fourth instars died in response to parasite exposure and the food-by-parasite interaction effect on the probability of fourth instars transforming to pupae over 48 h approached significance. Adult emergence reflected the above effects. These findings are discussed in the context of the Ae. aegypti/P. elegans host/parasite association and the role of entomopathogenic digeneans as natural enemies and their potential as agents in the biological control of mosquitoes.