Synaptonemal complexes (SCs) (structures involved in chromosome pairing during meiosis) were isolated and purified from rat spermatocytes for the purpose of biochemical and morphological analysis. Spermatocytes were lysed in a medium, containing Triton X-100, EDTA and DTT; the resulting swollen nuclei were disrupted by DNAse II, and the suspension was centrifuged through 1.5 M sucrose. The resulting preparation consisted for at least 60% of free SCs, as judged from electron micrographs of agar filtrates. The purified SCs still possessed lateral and transversal elements and attachment plaques. A small fraction also contained a central element. Particularly in diplotene SCs, the lateral elements clearly consisted of two subelements, which are connected by thinner fibres. The lateral elements may fall apart into a network of thinner fibres, presumably as a result of degradation during isolation. On SDS-polyacrylamide gels, the major protein components of purified SCs had relative mobilities (Mrs) of 67 to 60 and 57 to 55 kDa; in addition, there were minor proteins with Mrs of 90, 35, 33, 28, and 26 kDa, and varying amounts of histones. The 67 to 60 kDa proteins comigrate with lamins of rat liver pore complexes and laminae. A possible relationship between SCs and pore complexes and laminae is discussed.