A closed-loop, regenerative life support system must include a method for recycling organic waste materials. With a Controlled Ecological Life Support System (CELSS), this will be accomplished by decomposing the wastes and using the effluent to formulate a nutrient solution which supports food production by plants. The waste processing technology used may be either physicochemical or biological. Although the effluents from biological processors have been extensively evaluated as fertilizers for soil-based agricultural systems, few experiments have been conducted to evaluate their suitability in hydroponic applications. This paper describes the results of a series of experiments performed to evaluate effluent from an anaerobic bacterial reactor as a nutrient source for hydroponically-grown plants. Germination and initial seedling growth were found to be suppressed by pure effluent. Effluent dilutions of up to 90% still suppressed seedling growth by as much as 20%, although no effect on germination rate was evident at the highest dilutions tested. Lettuce plants were also grown to harvest size on fresh and aged waste effluent diluted to produce an electrical conductivity approximately equal to that of one-half strength Hoaglands solution. These growth experiments showed that fresh effluent suppressed growth by up to 80%. Aged effluent also suppressed growth, but only by about 20%. Ion chromatograph analysis of the effluents found that both effluents contained well over 200 ppm ammonia, as well as chloride concentrations that were over 10 times higher than half-strength Hoaglands solution. The implications of these findings are discussed.