A sample of 390 individuals from Ibiza (Balearic islands, Spain) was studied for the red-cell enzyme polymorphisms: esterase D (ESD), acid phosphatase 1 (ACP1), glyoxalase I (GLO), 6-phosphogluconate dehydrogenase (PGD), phosphoglucomutase 1 (PGM1) and adenylate kinase 1 (AK1). The following allele frequencies were observed: ESD*2 = 0.181; ACP*A = 0.249; ACP*B = 0.719; ACP*C = 0.032; GLO*2 = 0.556; PGD*C = 0.018; PGM1*2 = 0.235, and AK1*2 = 0.032. These results were compared with those reported from other Balearic populations. There was a heterogeneity between island samples in the ESD and PGD systems. In spite of this, the whole Balearic population could be differentiated from most European and circum-Mediterranean populations.