A new method for in situ pesticide quantitation is reported. Direct measurement of two pesticides (methoxychlor and N-(phosphonomethyl)glycine) spiked onto vegetables, has been carried out. The contaminant is detected by spraying the substrate with a probe solution of Nile Red and measuring the resulting solid state fluorescence. A portable, optical fiber-interfaced fluorimeter was constructed for this application. Glass and eggplant peel were used as the solid surfaces. The selectivity of this method, as well as matrix and optical effects of relevance have been studied and discussed. 95% Confidence limits of detection are 0.1-0.3 nmol and calibration is linear up to 4 nmol. Analysis of the two pesticides in mixtures was carried out based on mathematical treatment peaks whose wavelength of maximum intensity depends on the composition of the mixture.