In the present study, pancreas of rats were dissected and transferred to HEPES buffer (25 mM, pH 7.4). The control tissue pieces were kept in culture medium for one hour and the treated tissues were kept in same medium for 30 minutes and incubated with Insulin (10 nm and 100 nm) for another half hour, then tissues were transferred to Bouin‘s fixative (overnight at 40 ° Cc), cryosectioned (15 µm at -16 0 c) and subjected to immunocytochemical labeling with antibodies against Glucagon.Results:In the sections of control tissue, the Glucagon Immunoreactive Cells (GIC) were distinctly visible; on average 40-50 cells were counted in each islet. However in vitro treatment with 10 nm insulin caused 285.89 % increase in the GIC and was found to be highly significant (P< 0.001). Whereas in 100 nm Insulin treatment, 206.41% increase in GIC was seen, this was significant with the control but non-significant with 10 nm Insulin treatment