Two methods are described for the determination of caffeine, based on the formation of a caffeine-phosphomolybdate complex, decomposition of the complex and measurement of the equivalent molybdate by either differential-pulse polarography or atomic absorption spectrometry. Calibration graphs with a linearity range of at least 2–16 µg ml^–1 of caffeine in the final solution were obtained. The relative standard deviation is approximately 2% for both methods. The methods were applied successfully to the determination of caffeine in some analgesics.