A rapid screening method for the determination of carbaryl and propoxur using p-nitroaniline is described. Carbaryl and propoxur are determined spectrophotometrically: carbaryl forms a stable blue coloured species with diazotized p-nitroaniline in a fairly alkaline medium while propoxur forms a purple coloured species with the same reagent under similar conditions. The blue and purple coloured species are extracted into 3-methyl-1-butanol showing absorbance maxima at 605 and 540 nm, respectively. The relationship between absorbance and concentration is linear in the range of 0.12 - 0.96 ppm and 0.19–1.5 ppm, respectively for carbaryl and propoxur. The method can successfully be applied for the determination of carbaryl and propoxur to levels as low as 0.04 and 0.06 and 0.12 and 0.19 ppm in water and grain samples, respectively.