Rigorous new methods of protein sequence analysis have been applied to the lipocalins, a diverse family of ligand binding proteins. Using three conserved sequence motifs to search for similar patterns in a large sequence database, the size and composition of this protein family have been defined in an automatic and objective way. It has allowed the identification of an existing sequence, mouse 24p3 protein, as a lipocalin and the possible rejection of other putative members from this protein family. On the basis of this newly discovered homology, a possible function for mouse 24p3 protein is proposed.