Effects of hydrochloric acid concentration and duration of the Perls reaction on the intensity of the final product of this reaction were studied in isolated hepatocytes. The intensity was found to change slightly with the increase in HCl concentration from 0.1 to 2.0 N (in the mixture with the equal volume of 2% potassium ferrocyanide solution for each acid concentration). The highest intensity and specificity of the Perls reaction were observed within the range of HCl concentrations from 0.2 to 1.0 N. The staining maximum was achieved 1 h after the start of the reaction.