Abstract: Leech lectin 35 (LL35) is a calcium-independent galactoside-binding protein with a molecular mass of 35 kDa and binding properties similar to those of calcium-independent, galactose-specific lectins found in vertebrates, sponges, and nematodes. LL35 was initially isolated from membranes of the leech CNS; however, large amounts of this lectin were also extracted from the rest of the leech. Using affinity-purified antibodies to LL35, we report the immunocytochemical localization of LL35 in adult and embryonic leech. LL35 is developmentally regulated in epithelial, neuronal, and muscle tissue but is absent from glia. During embryogenesis, LL35 is highly expressed by a subset of sensory neurons, weakly expressed in epithelial cells, and absent from muscle. In the adult, LL35 is still present on the same sensory neurons but has become more abundant in epithelial cells lining the CNS and peripheral organs. LL35 also appeared on a muscle cell specifically located in the CNS but remained absent from peripheral muscle. The developmentally regulated distribution of LL35 in epithelial cells, neurons, and CNS muscles suggests a multifunctional role for this lectin with respect to these different cell types.