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The maximum number and diversity of macroinvertebrates from limestone-filled basket samplers were obtained by placing the samplers at a depth of 1 ft (0.3 m) below the water's surface for 8 weeks. The length of the exposure period had a greater effect on the number of organisms than depth of placement. The effects of longer exposure times (8 weeks, compared to 6 and 4 weeks) on the number and diversity of organisms inhabiting baskets were more pronounced during cold weather. In rivers during the summer months, samples contain a variety of aquatic insects, which contributed as much as 95 % of the total number of individuals. The occurrence of some macroinvertebrate species was related to the depth of sampler placement, e.g. the caddisfly Cyrnellus fraternus was more abundant at depths exceeding 4 ft (1.2 m); whereas the mayfly Stenonema interpunctatum was more abundant in samplers near the surface. The community diversity index (d) of collections on the same date varied by as much as two units depending on the depth of basket placement and length of exposure period, indicating that consistent practices in sampler installation and analysis are required for comparison of collections in water quality investigations. Baskets touching bottom accumulated greater amounts of sediments than surface samplers and generally showed greater variability within pairs. In the Ohio River, three replicate baskets can be expected (P = 0.95) to provide an estimate of the true mean number of macroinvertebrates within ±20% of the sample mean and contain 71 % of the taxa in 10 replicates. However, estimates of sampling precision based on replicate series may vary considerably depending on time, place, number of replicates and natural history of the organisms. Baskets filled with 2-in. (5.1-cm) diameter porcelain spheres collect samples comparable in total abundance and diversity to baskets filled with 2-in. (5.1-cm) diameter limestone. However, the taxonomic groups occur in different proportions on the two types of substrates. Hardboard multiplates of 1-ft² (0.1-m²) surface area with 1⁄8 (0.32) or ¼-in. (0.64-cm) spacings collect significantly greater numbers of individuals than porcelain multiplates with the same spacings. However, differences between samples from the same substrate type are not significant. Multiplates of the same surface area and plate spacing collect substantially the same number of taxa regardless of substrate type. Basket samplers (3.2 ft² = 0.3 m² surface area) collect a greater abundance and diversity of organisms than the standard 1 ft² = 0.1 m² hardboard multiplates. The performance of the samplers in terms of abundance and diversity is equalized, however, by increasing the surface area of the multiplate to that of the basket. [ABSTRACT FROM AUTHOR]