We have designed and built an apparatus for maintaining and renewing uniform suspensions of fine-grained sediment for laboratory experiments on the effects of suspended sediment on organisms. The suspensions are maintained with vertically reciprocating perforated plates driven by gearmotors. Suspensions with concentrations of up to 500 mg/liter were maintained to within about 15% of their mean concentration for periods of 5 to 7 days. The suspensions were completely replaced every 24 hours by periodic additions. The particles had a mass-weighted mean settling velocity of about 5×10−3 cm/sec.