The biochemical effects of two compounds i.e. theophylline and furosemide were studied on the glassy clover snail Monacha obstructa. Animals were treated with sub-lethal concentration (¼ LC₅₀) of each tested compound using contact (thin film) technique. Some biochemical parameters were measures at different periods after treatment.           Results showed that the two tested compounds gradually reduced the activity of aspartate amino transferase (AST) and peroxidase enzymes with the prolongation of periods after treatment, while the contrary occurred with alanine aminotransferase (ALT) as both compounds enhanced its activity proportionally than control. Concerning lactic acid dehydrogenase (LDH), results showed severe reduction in its level after 1, 2, 3 and 4 days post-treatment. Also catalase enzyme took adverse way as its activity increased in the 1^st, 2^nd, 3^rd and 4^th days for both compounds. On the other hand, levels of   the total protein and total lipid were significantly or insignificantly decreased post-treatment with the two tested compounds