COMPOUNDS OF THE FORMULA II: WHEREIN R2 IS THE SIDE CHAIN OF LEUCINE, ISOLEUCINE, CYCLOHEXYLGLYCINE, 0-METHYL THREONINE, 4-FLUOROLEUCINE OR 3-METHOXYVALINE; R3 IS H, METHYL OR F; RQ IS TRIFLUOROMETHYL AND RQ' IS H OR RQ AND RQ' DEFINE KETO; Q IS A P-(C1-C6ALKYLSULPHONYL)PHENYL- OR AN OPTIONALLY SUBSTITUTED 4-(C1- C6ALKYL)PIPERAZIN-1-YL-THIAZOL-4-YL- MOIETY HAVE UTILITY IN THE TREATMENT OF DISORDERS CHARACTERIZED BY INAPPROPRIATE EXPRESSION OR ACTIVATION OF CATHEPSIN K, SUCH AS OSTEOPOROSIS, OSTEOARTHRITIS, RHEUMATOID ARTHRITIS OR BONE METASTASES.