SUMMARYSmall amounts (5.6 or n‐2 kg a.i./ha) of aldicarb or oxamyl, incorporated in the soil before potatoes were planted in spring, controlled potato cyst‐nematodes(Heterodera rostochiensisandH. pallida)on susceptible cultivars equally well in sandy, peaty and silt loam soils. In soils treated with either nematicide, nematode numbers increased little or decreased; in untreated soils nematode numbers increased greatly. In contrast organophosphate nematicides, similarly applied, fenamiphos (proposed BSI common name forO‐ethyl‐O‐(3‐methyl‐4‐methylthiophenyI)‐isopropylamido‐phosphate), ethoprophos (proposed BSI common name for (O‐ethylS,5‐dipropyl phos‐phorodithioate), CGA 12223 (O,O‐diethylO‐[i‐isopropyl‐5‐chloro‐i,2,4‐triazoIyl‐(3)] phosphorothioate) and Dowco 275 (O,O‐diethylO‐(6‐fluoro‐2 pyridyl) phosphorothioate), were ineffective at one or more of the experimental sites. Potato yields were greatly increased by oximecarbamate or organophosphate nematicides