Certain dilute solutions of organic silver compounds, e.g. 0.001% silver proteinate, acting for a short time on cysts of the potato strain of Heterodera schachtii, cause increased numbers of larvae to emerge from the cysts when the latter are transferred to potato root excretion. More prolonged exposure of cysts to these solutions tends to result in a toxic effect which is also produced by more concentrated solutions. It is concluded that many more eggs in H. schachtii cysts are mature and capable of hatching than can be accounted for by ordinary larval liberation brought about by means of root excretion alone. Increasing periods of pre-treatment of cysts in tap water tend to produce increases in larval emergence, although this stimulation is probably of a different type from that given by silver compounds.