The effects of osmotic stress on water loss and subsequent desiccation survival of Anguina funesta second stage juveniles (J2), Rhabditis strongyloides (J2-J4), Aphelenchus avenae (J2-adult) and Heterorhabditis bacteriophora (J3) were investigated by incubating nematodes in sucrose gradients before exposure to 0% relative humidity (RH). Survival of A. funesta J2 was unaffected by osmotic stress and subsequent desiccation and juveniles seemed pre-adapted to both forms of dehydration. Heterorhabditis bacteriophora showed high tolerance to osmotic stress but all J3 were killed by exposure to 0% RH. Pre-exposure to osmotic stress improved desiccation tolerance in R. strongyloides and A. avenae but the stress levels that induced protective adaptations against desiccation were different for each species. Osmotically induced water loss was rapid in all four species and nematodes reached equilibrium after 4-12 h, their final water content being dictated by the osmotic pressure of the medium. A unique mechanism of osmotic adaptation occurred in R. strongyloides J2-J4 allowing juveniles to regain their initial hydration level.