Relative accuracy of sweep net sampling was compared with D-vac (D-vac, Riverside, Calif.) and absolute sampling methods for determining population densities of pea aphid, Acyrthosiphon pisum (Harris), Nabi. s spp., Hippodamia spp., and Chrysopa spp. in lentils ( Lens culinaris Medikus). Relative effects of the a biotic environment, predators, and time of sampling on population estimates also were determined during 2 yr. Original counts, area, and volume adjustments were used to evaluate accuracy of the sampling method. Volume adjustment was most accurate and was used in all subsequent evaluations. Sweep net estimates of pea aphid, Nabis spp., and Hippodamia spp. densities were similar to those obtained with absolute and D-vac sampling methods, although sweep net sampling consistently gave lower population estimates than those found for absolute sampling. In these experiments, the sweep net did not adequately sample the Chrysopa spp. in lentils. The time of sampling was significant when sampling for pea aphid; however, it was not as important for sampling of the three insect predators. Each year, sweep net samples were taken randomly at two locations in two fields every hour for 72 consecutive hours. The a biotic factors studied were light intensity, temperature, relative humidity, and wind velocity; Nabis spp., Hippodamia spp., and Chrysopa spp. were the predator groups studied. Light intensity was the only a biotic factor that was significantly correlated with pea aphid numbers over both years, whereas all four a biotic factors had significant correlations at low aphid densities in 1983. The diurnal sine of hour was significantly and positively correlated with number of aphids collected by sweep net each hour, whereas predator densities were significantly and negatively correlated with aphid densities over both years. Optimum sampling time for pea aphids in lentils can depend on the dominant predator group being sampled; however, for pea aphids and all predator groups, a sample taken in late morning is preferable when sweep net samples are taken.