The preparation of the N-Fmoc-O-Trt derivatives of serine, threonine and tyrosine is described. Their usefulness in peptide synthesis has been determined in the successful solid phase preparation of the partially protected ACTH (fragment 1-10) and peptide T 12. The latter, having six hydroxy amino acid side chains protected with Trt groups, can be quantitatively cleaved from the applied 2-chlorotrityl resin with simultaneous side chain deprotection.