Geneticvariability for leucylaminopeptidase among. C. rhizophorae from twolocalities in La Restinga Lagoon was examined using starch gel electrophoresis.There are three polymorphic loci for this enzyme, Lap-I, Lap-II and Lap-III,but only two were studied, Lap-II possessing three alleles and Lap-IIIpossessing six alleles. Allele distributions for Lap-III were dependent onlocation. The frequency of Lap-III⁹⁸ was higher at the centre of thelagoon (with greater temperature and salinity) than at the entrance (wheresalinity and temperature were lower). For Lap-III¹⁰⁰ the situationwas the opposite. Genotypic distributions at the Lap-II locus did not differsignificantly from Hardy-Weinberg expectations, whereas for Lap-III significantdifferences from equilibrium were detected. The large heterozygote deficiencyat the locus Lap-III is discussed in terms of the Wahlund effect, inbreeding,silent alleles and selection.