Stock assessment and three life history studies were conducted on humpback whitefish Coregonus pidschian and least cisco Coregonus sardinella in the Chatanika River and adjoining waters, near Fairbanks, Alaska during 1994 and 1995. The stock assessment occurred in a 102 km (64 mile) section of the Chatanika River during August 1994. Mark-recapture experiments were utilized to estimate abundance and stock composition of both species. The investigation was timed to correspond to the upstream spawning migration of both species, and to provide in-season estimates of abundance prior to the onset of a recreational spear fishery. An estimated 14,292 (SE = 1,215) humpback whitefish (>360 mm FL) were present in the study area. The assessed stock was characterized by a high proportion of large humpback whitefish (>430 mm FL) with ages 8, 9, and 10 predominating. An estimated 29,557 (SE = 3,410) least cisco (>290 mm FL) were present in the study area. The assessed stock was predominated by ages 3 and 5 least cisco. Survival estimates from August 1993 to August 1994 were 41.8 and 84.6 percent for least cisco and humpback whitefish, respectively. These survival estimates assume that least cisco and humpback whitefish are consecutive year spawners. Three supplemental investigations attempted to gather life history data to examine geographic closure of the Chatanika River whitefish stocks. A migration study found that at least 10 percent of least cisco present in the lower Chatanika River during early September eventually travel upstream to areas where a fishery occurs. A second study attempted to estimate maturity among adult-sized fish in an effort to detect non-consecutive spawning. In the course of this study, fish could not be categorized using external examinations because many fish failed to reach spawning condition. A radio telemetry study on humpback whitefish sought to characterize the geographic range with respect to time, areas of overwintering, availability to traditional subsistence fisheries, and the annual stock assessment program. High levels of mortality among radio-tagged fish precluded objective estimates.