A number of gas chromatograph detectors and columns were tested for determining concentrations of phosphine in air occurring during fumigation. For the range 0.02 to 3 mg/l the beta-ionization argon detector proved most suitable using the conditions described, giving results with an accuracy of ± 2 per cent. After standardization against dilute mixtures of phosphine in argon, concentrations can be read directly form a calibration chart to give results within minutes of sampling during fumigations. The thermionic (phosphorus) detector is more sensitive but requires very finely controlled condition more applicable to laboratory work.