The effect of cold 5N HCl (25°C±3) and hot (60°C) 1N HCl Feulgen hydrolysis procedures were compared for retention of tritiated thymidine as well as dye binding. Phytohemagglutinin (PHA) stimulated human lymphocytes were cultured using conventional procedures, pulse labeled with one microcurie 3HTdR per ml cell suspension, stained with Schiff using conventional (1N HCl-60°C) and cold (5N HCl-25°C) procedures. The developed autoradiographs were then analyzed as to mean grain count over-all labeling index and qualitative colorometric properties. The results indicate that the plateaus for maximal retention of 3HTdR as well as binding of Schiff reagent in phytohemagglutin (PHA) stimulated lymphocytes is best achieved using cold hydrolysis times as recommended in this study.