A comparison was made of three methods for gentamicin assay; a modification of the radioenzymatic transferase technique, which was used as the reference method; EMIT autocarousel; and EMIT quantitative single test (QST). Correlation of both EMIT systems with the radioenzymatic method and with each other gave acceptable correlation coefficients, 0.955-0.975, for the range of concentrations tested. The coefficients of variation for within assay studies were between 3.3 and 4.9 for all three methods. Both EMIT systems provided rapid results, within minutes, albeit at a higher cost than the radioenzymatic assay. The radioenzymatic technique although cheaper with regard to the cost of materials involves considerably more technical time and effort and might not be considered suitable for samples received out-of-hours. However the combination of both EMIT systems provides facilities for batch and one-off sample tests and the ease of operation and rapid results are suited to out-of-hours operation.