The direct toxicity of the fungicide benomyl to eggs and immature stages of a predatory mite Amblyseius fallacis (Garman) was assessed by residue and slide-dip test methods. The effect on the predators resulting from ingestion of benomyl-treated two spotted spider mites, Tetranychus urticae Koch, also was evaluated. Benomyl was moderately ovicidal and considerably more toxic to immature predators by residual contact than by direct contact. Secondary poisoning through the prey caused permanent depression of oviposition. This effect was negatively correlated with the length of time that predators were exposed to the treated frey. Due to the moderate to severe toxic effect of benomyl on various life stages of A. fallacis, this compound should not be applied to apple trees at times when predators are controlling prey mites.