The aim of the present study was to develop a simple method to measure ranitidine, using 100 microL of plasma, by high-performance liquid chromatography with a Symmetry C(18) column and UV detection at 313 nm. Linearity was assessed in the range from 50 to 1500 ng ml(-1) and had a correlation coefficient of 0.999. The inter- and intra-day coefficients of variation were less than 7%. The limits of detection and quantitation were 5 and 15 ng ml(-1), respectively. Drug levels were determined satisfactorily in three patients. A simple and reliable method was developed which uses a microvolume of plasma, particularly useful in low-weight children.