Abstract: TPP II (tripeptidyl peptidase II) inhibitors are useful in the treatment of autoimmune and/or inflammatory diseases, for example Systemic Lupus Erythematosus, Rheumatoid Arthritis, Multiple Sclerosis, Sjögrens Syndrome, Diabetes Mellitus Type I or II, Psoriasis, Eczema, Ulcerous Colitis, and Chron's Disease, or transplant rejection. Suitable compounds comprise tripeptide compounds of general formula RN1, RN2, A1, A2, A3 and RC1 are as defined herein, and which include for example the tripeptide sequences GLA and GPG.