The homogeneity of analytical sample should be checked prior to analysis. Sample processing, which may be source of systematic errors, is the procedure used to make the analytical sample acceptably homogenous with respect to the analyte distribution. For a quick quantify the analyte in the extract without clean-up, vertically cut tomato samples were surface treated with C-14-chlorpyrifos, communited and extracted. Then C-14-chlorpyrifos radioactivity was determined in the replicate analytical portions of different size and uncertainty of sample processing was determined. F test revealed that, the processed samples were well-mixed. The typical sampling constant (K-S), was calculated as 1.24 kg.