QPS performs mass balance studies to comprehensively evaluate the routes of excretion of compounds through urine, bile, feces, and expired air. Typically a group of animals will also be dosed to collect blood/plasma samples for the evaluation of systemic pharmacokintetics of total radioactivity. Occasionally, specific tissues are collected to evaluate exposure in specific tissues.

These studies are often performed using intact animals, jugular/femoral vein-cannulated animals and bile duct-cannulated animals. Isotopes including 3H, 14C, 32P, 33P, 35S, 45Ca and 125I have been approved for tests on rodents. QPS performs GLP and non-GLP mass balance studies in rodents and non-rodent studies are performed through QPS partner laboratories.

All samples collected in mass balance studies are often saved for metabolite profiling and identification purpose.