In Brassica, recognition and rejection of 'self' pollen is rapid, occurring at the stigmatic surface usually prior to pollen germination and is mediated by products of the S (incompatibility)-locus. Two polymorphic stigmatically-expressed S-locus genes, thought to participate in the perception of 'self' pollen have been characterized to date. One, the SRK (S-receptor kinase) encodes a transmembrane receptor kinase likely to be activated by the binding of an S-specific pollen-borne ligand. The other, SLG (S-locus glycoprotein), encodes a secreted cell wall glycoprotein whose role in self-incompatibility (SI) is less clear and increasingly questioned. The pollen coating in Brassica is known to carry the male determinant of SI as well as factors crucial for competent pollen-stigma interactions. Characterization of the coating has revealed the presence of several families of gametophytically expressed small cysteine-rich proteins (PCPs - pollen coat proteins). PCPs are strongly implicated in playing a central role in SI and other aspects of the pollen-stigma interaction. PCP-A (for PCP, class 'A') class proteins have specific affinities for stigmatic S- and S-related proteins and these, along with other recently characterized groups of PCPs, are abundant components of fractions having S-specific activity in pollination bioassays. The role of the pollen coating, and particularly PCPs and their expression patterns, will be discussed in the perspective of the pollen-stigma interaction and SI. (C) 2000 Annals of Botany Company.