Allozyme genetic variation in larvae and adults of the crabsRhithropanopeus harrisii, Sesarma cinereum, andS. reticulatum was investigated. InRhithropanopeus from North Carolina, Maryland, and Maine essentially no geographic variability was detected at 15 allozyme gene loci, all but perhaps one of which was monomorphic in the samples utilized. There was also no life cycle variability in enzyme expression among zoeae, megalopa, and adults other than assay differences. The two species ofSesarma, all collected in North Carolina, also showed no life-cycle variation. Three of 13 loci were polymorphic inS. reticulatum, 0 of 13 inS. cinereum, and 0 or 1 of 15 inR. harrisii.