Water extracts from saturated composted municipal refuse rendered sting nematodes, Belonolaimus longicaudatus, immotile after immersion for 12 hr. Extract concentrated to 33% o f its original volume rendered all o f the 50 sting nematodes tested immotile in 3 hr. The effect of compost extract was slightly reduced by cation exchange and greatly reduced by peroxide digestion of the organic fraction. Immotile nematodes were transferred from compost extract to distilled water after 24 hz and 60% regained motility, but after 144 hr none regained motility.