A successful design of peptidomimetics must come to terms with chi-space control. The incorporation of chi-space constrained amino acids into bioactive peptides renders the chi(1) and chi(2) torsional angles of pharmacophore amino acids critical for activity and selectivity as with other relevant structural features of the template. This review describes histidine analogues characterized by replacement of native alpha and/or beta-hydrogen atoms with alkyl substituents as well as analogues with alpha, beta-didehydro unsaturation or C-alpha-C-beta cyclopropane insertion (ACC derivatives). Attention is also dedicated to the relevant field of beta-aminoacid chemistry by describing the synthesis of beta(2)- and beta(3)-models (beta-hHis). Structural modifications leading to cyclic imino derivatives such as spinacine, aza-histidine and analogues with shortening or elongation of the native side chain (nor-histidine and homo-histidine, respectively) are also described. Examples of the use of the described analogues to replace native histidine in bioactive peptides are also given.