Quantitative immunoelectron microscopy (QIEM) is dependent on the reliability of preparative techniques for both efficient immunolabeling and consistent quantitative results among series of immunostained sections. The present study compared Lowicryl K4M and Epon embedding after identical fixation and dehydration of rat somatotrophic secretory granules. Labeling intensity, diameter, roundness, uptake of uranyl acetate, and gray value were measured with computer assisted image analysis. Lowicryl-embedded granules showed the highest labeling densities after conventional fixation and Progressively Lowering Temperature (PLT) dehydration, but values were not consistent in a series of immunostained sections. A lower but more uniform level of immunostaining was seen in Epon-embedded sections when tissue was cryofixed and physically dehydrated. Gray value measurements from micrographs from both embedding media confirmed the better contrast of Epon sections and the different reliefs of the granule surfaces. This study emphasizes the importance of complete comparisons of preparative techniques for QIEM for reliability and reproducibility.