[snip problems with dimerization of peptide] peptides with a CYS tend to dimerize even when lyophilized. Detect the free CYS with Ellmans reagent. If dimerized and the peptide too small for dialysis (and thus DTT treatment) you could try the Reduce-Imm column from Pierce - it is fundamentally an immobilized DTT on sepharose. Keld.