A second-year organic chemistry laboratory experiment to introduce students to general concepts of medicinal chemistry is described. Within a single three-hour time window, students experience the synthesis of a biologically active small molecule and the assaying of its biological toxicity. Benzodiazepine rings are commonly found in antidepressant therapeutics, including Valium and Xanax. This experiment involves the one-step synthesis of a 1,5-benzodiazepine derivative via the condensation-cyclization of "ortho"-phenylenediamine with two equivalents of acetone. Following its isolation, the toxicity of the benzodiazepine product is evaluated via a brine shrimp assay, which allows students to rapidly observe differences in biological activity among varying benzodiazepine concentrations. (Contains 1 figure and 1 scheme.)