Immobilised 1,3-specific lipase from Rhizopus arrhizus was used as catalyst for the esterification of DL-glycero-3-phosphate and fatty acid or fatty acid vinyl ester in a solvent-free system. With lauric acid vinyl ester as acyl donor; a(W) < 0.53 favored the synthesis of lysophosphatidic acid (1-acyl-rac-glycero-3-phosphate, LPA1) and the spontaneous acyl migration of the fatty acid on the molecule. Subsequent acylation by the enzyme resulted in high phosphatidic acid (1,2-diacyl-rac-glycero-3-phosphate, PA) formation and high total conversions (> 95%). With oleic acid, maximum conversions of 55% were obtained at low water activities. Temperatures below melting point of the product favored precipitation and resulted in high final conversion and high product ratio [LPA/(PA + LPA)]. Thus, LPA was the only product with lauric acid vinyl ester as acyl donor at 25 degrees C. Increased substrate ratio (DL-glycero-3-phosphate/fatty acid) from 0.05 to 1 resulted in a higher ratio of LPA to PA formed, but a lower total conversion of DL-glycero-3-phosphate. Increased amounts of enzyme preparation did not result in higher esterification rates, probably due to high mass-transfer limitations.