AbstractAs part of a structure‐activity relationship study of ribonuclease, focussing on the role of histidine‐119 in the active centre, two tetradecapeptides were synthesized by the solid‐phase method: [His119]RNase 111‐124 and the corresponding analogue in which His‐119 is replaced byLhomohistidine.While the [Hhis119] analogue has almost the same binding capacity towards RNase 1‐118 protein as the natural peptide, the resulting complex is devoid of any catalytic activity when RNA or 2′,3′‐CMP is