Hatching from cysts and eggsacs of six successive generations of Heterodera cajani produced on cowpea during a single growing season in the glasshouse was compared in distilled water, soil leachate and host root diffusate from four week old plants. The majority of eggs in eggsacs hatched within 7 days in all treatments and there were no differences between generations. Hatch from cysts in all treatments was similar over the first four generations but the fifth and sixth generations, produced on senescing plants, showed a marked dependency on host root diffusate for hatch. The ratio of eggs in eggsacs to eggs in cysts decreased with each succeeding generation and a comparison between third and sixth generations indicated that, in the older generation, more lipid reserves are partitioned into the encysted J2 than into the J2 in eggsacs. The results are discussed in the context of the survival requirements of H. cajani in the absence of a host.