The lateral elements (LEs) of synaptonemal complexes (SCs) of the rat contain major components with relative electrophoretic mobilities (Mr s) of 30000-33000, which are the products of a single gene. After one-dimensional separation of SC proteins on polyacrylamide-SDS gels, these components show up as two major bands, whereas upon two-dimensional electrophoresis they are resolved in at least 24 spots, which focus at pH 6.5 to 9.5. In this paper we show that these spots represent phosphorylation variants. For the analysis of the phosphorylation of the 30000- to 33000-Mr SC components during progression through meiotic prophase, we developed a procedure for isolation of fractions of testicular cells of the rat that are enriched in separate stages of meiotic prophase. Analysis of the 30000- to 33000-Mr SC components in these fractions by two-dimensional electrophoresis and immunoblotting showed that phosphorylated variants of the 30000- to 33000-Mr SC proteins occur throughout meiotic prophase. However, the extent of phosphorylation changes between early and mid-pachytene, when one phosphate group is probably added to each of the variants.