The sedentary ciliate fauna living on the body surface of Gammarus tigrinus and G. pulex from Dutch freshwater habitats has been investigated. Fourty-seven ciliate species are found, of which 43 belong to the order Peritrichida, suborder Sessilina, 3 belong to the order Suctorida and 1 belongs to the order Chonotrichida. Two new species in the genera Intranstylum and Pseudocarchesium are described. It appears that there is a seasonal variation in the number of epizoic ciliates as well as in species composition. In general, the species with a contractile stalk are found on external, often fast-moving, body parts. Species with a noncontractile stalk seem to prefer more quiet and sheltered positions. After ecdysis there is a succession of the genera Epistylis and Zoothamnium, the latter becoming dominant on older exoskeletons.