OBJECTIVE The pharmacokinetics of iopromide were analysed using a two-compartment model. The optimal point of time for blood withdrawal for calculation of a one-sample clearance was determined. METHODS Plasma concentration of iodine was measured up to 8 h postinjection (p.i.) in 62 adult patients who received 120 ml iopromide for computed tomography (CT). A two exponential function was fitted by a weighted least error square method. As reference method, clearance was calculated from this function and the injected amount of iodine. Empirical parameters for calculation of one-sample clearance were determined. This one-sample clearance was compared with one-sample clearance calculated according to formulas developed for Tc99m-DTPA by Jacobsson as well as a two sample method. RESULTS Total distribution volume of iopromide was calculated as 0.242 Lkg(-1)+/- 5.9%. A high correlation of all one-sample method and the two-sample method with reference to clearance was found. Best estimation of iopromide plasma clearance was achieved by determining one-sample clearance 270 or 285 min p. i. with SD(y.x) of 5.8 ml min(-1). CONCLUSIONS After administration of 120 ml iopromide, one-sample plasma clearance can be calculated with low estimation error taking one blood sample at an appropriate time point. Late phase pharmacokinetics of iopromide found in the present study showed to be virtually identical to results published for iohexol and Tc99m-DTPA.