The plasma pharmacokinetic characteristics of the chemopreventive isothiocyanate sulforaphane were determined in six human volunteers following single and repeated intake of raw broccoli. Initially, an analytical method utilising LC-MS/MS, capable of determining low levels of sulforaphane in human plasma was developed and validated. The plasma profile of the isothiocyanate best fitted a two-compartment pharmacokinetic model. Sulforaphane was rapidly absorbed with peak plasma levels being attained within 1.5h, and was characterised by a long terminal elimination phase. Repeated intake of broccoli had no impact on the pharmacokinetic behaviour or plasma levels of sulforaphane, and there was no evidence of accumulation.