Anti-phospholipids represent a heterogeneous family of antibodies able to react with the negatively charged phosphodiester groups of phospholipids. It includes the antibodies directed against the cardiolipin moiety of the VDRL antigen, the antibodies reacting with the phospholipids of the prothrombin activator complex and the antibodies able to react with solid phase cardiolipin. Data are reported indicating that reagins share distinct characteristics in comparison to the autoimmune anti-cardiolipin antibodies (ACA). On the contrary anti-phospholipid antibodies responsible for lupus-like anticoagulant activity display a quite similar reactivity with ACA, even if a complete overlapping cannot be demonstrated. The relationships between ACA and anti-DNA antibodies are also reported. The biological and clinical significance of these crossreactivities are discussed.