Soluble galactoside-binding lectins could play a key role in vertebrates by specifical binding to complementary glycoconjugates. 2. Their expression and localization are developmentally regulated. 3. They constitute a large family of structurally related proteins which contain a series of conserved aminoacids. 4. Their functional role could vary from an organ to another, and the same lectin may probably mediate several biological activities.