The chemical composition of the solvent extracted fixed oil of black cumin (Nigella sativa L.) seeds was determined by capillary GC and GC/MS. Thirty-two fatty acids (99.9%) have been identified in the fixed oil. The major fatty acids were linoleic acid (50.2%), oleic acid (19.9%), margaric acid (10.3%), cis-11,14-eicosadienoic acid (7.7%) and stearic acid (2.5%). The effect of black cumin oil on in vitro percutaneous absorption of the model lipophilic drug carvedilol was investigated using excised rat abdominal skin. Transdermal flux, permeability coefficient and enhancement factor were calculated for different concentrations of oil in isopropyl alcohol. Black cumin oil (5% v/v) exhibited the highest enhancement in permeation. The increase in the permeability of the drug is due to increased drug diffusivity through the stratum corneum under the influence of black cumin oil. A higher content of linoleic acid (and other unsaturated fatty acids) in the oil has been postulated to be responsible for the enhancement of in vitro percutaneous absorption of the drug.