A double-blind, randomized, placebo-controlled study has been carried out in order to assess the effects of the new topical cutaneous formulation, diclofenac hydroxyethylpyrrolidine (DHEP) plaster. Sixty patients (10 M + 50 F, mean age 56.6 yrs) suffering from local inflammatory processes in peri-articular/tendinous and/or extra-articular sites were involved in this study and randomly given either DHEP plaster or placebo plaster. Plasters were applied and left on the site of inflammation b.i.d. (at 8 a.m. and 8 p.m.) for 14 days. Patients under stabilized systemic treatment with NSAIDs, glucocorticoids and/or basic therapy for over 2 months, maintained this treatment unchanged during the course of the study. Patients were examined on days 3, 5, 7 and 14. The effects of the treatments were assessed using subjective, semi-quantitative (provoked pain, peri-articular swelling, doctor-patient judgement, telethermographic index) and quantitative variables (spontaneous pain measured using a visual analogical scale). In the peri-articular pathologies, spontaneous and provoked pain decreased faster and in a clinically relevant manner in the group treated with DHEP plaster compared to the control group (p < 0.01). Local inflammation, objectively evaluated using the telethermographic index, showed consistent reduction during the study which was statistically significant from day 3 onwards and significantly different compared to the control group. Global assessment of efficacy, expressed by the investigator and the patients, was significantly better (good to excellent after only 7 days in 70% of the cases) in the DHEP group compared to the placebo group. In the extra-articular pathologies, results similar to those reported earlier were obtained.(ABSTRACT TRUNCATED AT 250 WORDS)