The mode of cellular toxicity of aqueous extract of Fadogia agrestis stem in male rats was investigated. Rats were grouped into four: A, B, C and D where A (the control) received orally 1 mL of distilled water; B, C and D (test groups) received orally 18, 50 and 100 mg/kg body weight of the extract, respectively, for 28 days. Infrared spectroscopy indicated the presence of hydroxyl (OH) and primary amine (CONH). Clinical toxicity symptoms such as respiratory distress, epistasis, salivation, hypo- and hyperactivity were not observed at any period of the experiment. No mortality was also recorded. Extract administration significantly reduced (p < .05) the activities of alkaline phosphatase, lactate dehydrogenase and gamma glutamyl transferase in the liver and kidney with corresponding increases in the serum. Serum malondialdehyde also increased significantly in all the extract-treated groups. The liver and kidney body weight ratios of the extract-treated animals compared well (P > .05) with their controls throughout the experimental period. The extract did not cause any swelling, atrophy or hypertrophy of the organs. The other evidence in this study suggests disruption of the ordered lipid bilayer of the plasma membranes of the hepatocytes and nephrons. This might have resulted from peroxidation of the polyunsaturated fatty acids on the membranes of the hepatocytes and nephrons made possible by the functional groups or the product of metabolism of the extract. This may be responsible for the compromise of the integrity of the plasma membranes of the hepatocytes and nephrons.