Populations of the troglobitic (i.e., obligatory cavernicole) amphipod Crangonyx antennatus living in two distinct aquatic habitats were examined for possible morphological variation. Collections were made seasonally for one year in six Lee Co., Virginia caves, three with mud-bottom pools and three with small gravel-bottom streams. Environmental parameters thought to influence population variation were recorded for each of the six caves. Body length of mature amphipods was found to be greater in the mud-bottom pool habitats, whereas stream amphipods possessed more first antennal segments per unit body length. Variation was also observed in integument coloration; stream amphipods were characterized by a brownish integument and pool amphipods a whitish integument. Differences in the type and amount of available food in the two habitats is considered the most important environmental parameter affecting morphological variation. The population variation noted between habitats is believed indicative of the adaptive flexibility of this vagile troglobitic species.