A method is described for the determination of low levels of selenium in soils. An extract of the soil in nitric acid and orthophosphoric acid is prepared. An aliquot is oxidised with potassium persulphate at 100 °C, at which temperature the loss of selenium is minimal. The excess of nitric acid is removed by evaporation and 50 per cent. hydrochloric acid is added to reduce selenate. The selenite produced is complexed with 2,3-diaminonaphthalene and the resulting 4, 5-benzopiazselenol is extracted with cyclohexane. Sodium sulphate is added to removed interfering substances and the selenium complex is determined fluorimetrically. Selenium in soils down to 0·04 p.p.m. can be determined to within ±0·1 p.p.m.