This paper describes a high-performance liquid chromatographic method with fluorescence detection for the analysis of methyl-beta-cyclodextrin (MEBCD) in plasma and cell lysate, after in situ complexation with 1-naphthol. The size-exclusion HPLC column packed with TSK 3000 SW gel, was equilibrated with an eluent mixture composed of methanol and purified water (2:98, v/v) containing 10(-4) M 1-naphthol as a fluorophore. The detection is based on fluorescence enhancement caused by the formation of inclusion complexes and was performed at 290 and 360 nm for excitation and emission, respectively. The method involved a simple treatment of the samples with chloroform. Daunorubicin was used as internal standard. Limits of quantitation were 0.8 microM in plasma and 0.5 microM in cell lysate. Detection limits of 0.5 microM (50 pmol) and 0.3 microM (30 pmol) were obtained for MEBCD in the two media, respectively. Linear detection response was obtained for concentrations ranging from 1 to 100 microM in plasma and cell lysate. Recovery from plasma proved to be more than 40%. Precision, expressed as C.V. was in the range of 4 to 11%. Accuracy ranged from 89 to 105%.