Dimethylselenide (DMSe) and dimethyldiselenide (DMDSe) were determined in plant and water samples by capillary gas chromatography using microwave induced-plasma atomic emission spectrometry for detection. The analytes were leached from the solid samples into methanol by using an ultrasonic probe, and a portion of the extract was preconcentrated by means of a purge-and-trap system before being chromatographed. The analytes were directly purged from the water samples in the presence of 6% (v/v) methanol. Element-specific detection and quantification was carried out by monitoring the selenium (196 nm) emission line. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were 0.9999 for both analytes. Detection limits of 0.8 and 1.1 ng l(-1) were obtained for DMSe and DMDSe, respectively, for water samples. For plant materials, the detection limits calculated for 0.5 g samples were 0.3 and 0.4 ng g(-1) for DMSe and DMDSe, respectively. Concentration levels of DMSe ranging from 1.2 to 4.2 ng g(-1) were found in some of the plant materials analyzed. No DMDSe was found in any of the samples. The accuracy of the method was checked by analyzing different spiked water and plant samples.