The TRANSIL Brain Absorption kit estimates the binding of drugs to brain tissue and predicts the disposition of drugs into brain. It measures the affinity of drugs to reconstituted porcine brain membranes. The brain membrane affinity is used to estimate the brain tissue binding and to predict the brain-to-plasma distribution via a hybrid model that also incorporates the drug’s polar surface area and its plasma protein binding. Internal quality controls provide easy assessment of recovery, experiment and data quality.