SUMMARYIn sandy clay loam under glass 11.2 kg a.i. Du Pont 1410 alone or with 448 kg Di‐Trapex CP/ha, 441 kg dazomet with 448 kg Telone or 448 kg Di‐Trapex CP/ha, prevented potato cyst‐nematodes,Heterodera pallida, increasing on KNVF tomato rootstocks. In the heated glasshouse where the soil was treated with 441 kg dazomet/ha alone, the nematodes increased in the top 10 cm of soil, whether the soil was sealed with Polythene sheeting or water and whether dazomet was applied as dust or prill (small granules). Methyl bromide at 1276 kg/ha did not control the nematodes in soil 20–30 cm deep in one of the treated plots. Tomatoes grew well after all treatments except Du Pont 1410 which had little, if any, effect on grey sterile fungus (Pyrenochaeta lycopersici). Dazomet with Telone or dazomet with Di‐Trapex CP inhibited root damage by t