This experiment was performed to evaluate the morphological responses of the mucosa of the mouse appendix, inoculated with Ehrlich carcinoma cells in the inguinal area, following administration of Acriflavine-Guanosine Composition (AG60). Healthy adult ICR mice weighing 25 gm each were divided into normal, experimental control and AG60 treated group. Experimental control and AG60 treated groups, mice were subcutaneously inoculated with 1 x 10(7) Ehrlich carcinoma cells in the inguinal area. From next day after the carcinoma cell inoculations, 0.2 mL of saline or AG60 (5 mg/kg/0.2 mL) were injected subcutaneously to the animals every other day, respectively. The day following the 7 th injection of saline or AG60, each mouse was injected with a single dose of 0.7 microCi/gm of methyl-3H-thymidine (25 Ci/mmol, Amersham Lab., England) through tail vein. Seventy minutes after the 3H-thymidine injection, animals were sacrificed, and appendix tissues were fixed in 10% formalin solution for light microscopy. The number of the labeled mucosal epithelial cells of the appendix were observed and evaluated. For the electron microscopic study, the tissues were fixed in 2.5% glutaraldehyde-1.5% paraformaldehyde solution, followed by post-fixation with 1% osmium tetroxide solution. Ultrathin sections were counter stained with uranyl acetate-lead citrate solutions, and observed. On light microscopic observation of experimental control and AG60 treated mice, did not show any remarkable morphological alterations on the mucosae. On autoradiographic study, number of the labeled cells within 3.5 mm width mucosae of normal control, experimental control, AG60 treated mice were 362.2+/-56.12, 350.7+/-42.65 and 90.7+/-33.48, respectively. On ultrastructural observation of the experimental control and AG60 treated mice, general morphologies of the epithelial cells of appendix were similar. But intranuclear filamentous structures, intramitochondrial dense granules, and myelin figures were occasionally observed in the absorptive cells of AG60 treated mice than control ones. Above results show that AG60 suppress the DNA synthetic activity of the mucosal epithelial cells of mouse appendix, but did show slight ultrastructural alterations in the absortive cells. These results suggest that AG60 is one of effective anticancer drug for the cytostatic therapy.