The electrochemical behavior of the benzodiazepine halazepam was investigated by differential pulse and tast polarography in water/methanol solutions. Reduction of halazepam was performed in one irreversible, diffusion-controlled step using Britton-Robinson buffers. The peak potential at pH 8.5 and a 10% methanol/water solution was −1.10 V (vs Ag/AgCl/3 M KCl). Halazepam can be determined at nanomolar levels, using adsorptive stripping voltammetry. Applicability of tests on commercial preparations and human urine are described. The detection limit was 25 ng ml−1 of urine for an accumulation time of 20 s; the mean standard deviation was lower than 3.0% for 264 ng ml−1 samples (n = 3) with a mean recovery of 97%. A study of the interaction of human serum albumin with halazepam and diazepam has been performed by differential pulse polarography; a lower affinity of halazepam for HSA was established.