The effects of low temperature treatment of Heterodera glycines eggs and the interaction of this treatment with egg condition and cyst influences were examined in vitro. Exposure of eggs to 5°C for 1 week followed by a return to normal culture temperature resulted in a 25-33% reduction in hatch after 2 weeks at 28°C but there was no effect on the timing of hatch. Hatch from encysted eggs was 40% lower than from free eggs at 2 weeks, and hatch from low temperature-encysted eggs was more than 60% lower during the same period. Encystment also altered the timing of hatch relative to free eggs from the same cohort. Hatch from free eggs in the presence of cyst contents was accelerated relative to free eggs without cyst contents, but the total cumulative percent hatch was not increased. Reduction in hatch as a result of low temperature treatment was significant only if the treatment was applied prior to the first juvenile stage (J1). J1 were not affected relative to the hatch of second-stage juveniles (J2). However, the effect of low temperature on earlier stages was not detected until development ceased at early J1 and later J1. Also, low temperature treatment affected the apparent locomotion of some newly hatched J2; 16-fold more J2 from treated eggs were retained on 30 μm pore sieves than those from control eggs. The depression of hatch by low temperature egg treatment was apparently the result of the residual effects on early embryo stages, leading to arrest of development prior to J2.