BACKGROUND 'Home made' ultra-rapid urease tests are used extensively in the Asia Pacific region. Data on the reliability of these 'home made' tests are limited. OBJECTIVE To evaluate the effect of test duration on the sensitivity and specificity of a self-prepared biopsy urease test for the detection of Helicobacter pylori. METHODS Using histology as the 'gold standard', the effect of test duration on the sensitivity and specificity of a self prepared urease test for the detection of H. pylori was evaluated in 411 consecutive patients undergoing upper gastrointestinal endoscopy. RESULTS Histology was positive for H. pylori in 217 of the 411 patients (52.8%). Within 24 hours of retrieving the specimen, 189 (87.1%) of the histology positives and 174 (89.7%) of the histology negatives were correctly identified by the urease test. Of the H. pylori positives, 72.0%, 81.0%, 89.9% and 100% were detected by the urease test within one minute, five minutes, three hours and 24 hours respectively. Thus, sensitivities of the urease test at one minute, five minutes, three hours and 24 hours were 62.7%, 70.5%, 78.3% and 87.1% respectively. Corresponding figures for the specificity were 93.8%, 93.3%, 92.3% and 89.7% respectively. Using a receiver-operating characteristic curve, an optimal combination of sensitivity and specificity was obtained when the urease test was read at 24 hours. CONCLUSIONS While the biopsy urease test was positive in most cases within a minute, better results could be obtained if the test continued to be read over a 24 hour period.