Olefin tethers of variable length, introduced into a natural amino acid (side-chain of Ser, Cys; N-terminus of Arg; C-terminus of Phe and Tic; and in both the side-chain and either the N- or C-terminus of Ser, Cys and Tyr), undergo metathesis on treatment with Grubbs' second generation catalyst. Side-chain linked dimers of Ser, Cys and Tyr were obtained by cross-metathesis, while olefin installation at the N- and C-terminus led to dimers of Arg and Phe (or Tic), respectively. Ring-closing metathesis of the doubly alkenylated derivatives of Ser, Cys and Tyr gave 12-, 20- and 24-membered macrocycles.