SUMMARY The technique for the growth of calcium oxalate crystals by the slow addition of calcium and oxalate ions to a medium was standardised. A quantitative method of assessing crystal growth was developed by estimating the calcium content of the crystals using a modified Auto-Analyser procedure. Various substances were added to a buffer medium and human urine in order to study their effects on the growth of calcium oxalate crystals. Contrary to findings by other workers many of the compounds which were effective inhibitors in the buffer medium did not suppress crystal growth in human urine. Malachite green, sodium pyrophosphate and to a lesser extent tetracycline and Teepol were among the few effective inhibitors in both urine and buffer medium.