The two standard tests for the initial diagnosis of non-gonococcal urethritis (NGU), microscopic examination of gram stained urethral smears and the two glass urine test, have the disadvantage of being insensitive and subjective. The leucocyte esterase test detects enzymes specific to polymorphonuclear leucocytes and can therefore be used as a sensitive indicator of pyuria. This study sought to evaluate its use as a rapid, sensitive, and non-subjective method of screening for NGU. Of the 81 men with urethral symptoms in the study group, 26 had more than 5 polymorphonuclear leucocytes per high power field (x 1000) and all 26 were leucocyte esterase test positive; whereas 55 had fewer than 5 polymorphonuclear leucocytes per high power field, but 29 (53%) of them had a positive leucocyte esterase test result. In addition, 25 patients in the study group yielded Chlamydia trachomatis on culture. Of these 25, 24 (96%) were leucocyte esterase test positive, whereas only 11 (44%) were Gram stain positive. All 40 patients in the control group (without urethral symptoms or signs) were leucocyte esterase test negative. The leucocyte esterase test is thus a rapid, sensitive, and non-subjective screening aid in the diagnosis of NGU.