Brief intervention (BI) in smoking has been shown to be an effective way of stopping smoking in the general population. BI involves medical advice given to each smoking patient, with complementary information on the effects of smoking on the body and methods of giving up the habit. Patients who come to the clinic with respiratory disease may be especially receptive to BI since the strong link between their symptoms and smoking may increase their motivation for cessation. A BI protocol on smoking was applied in 285 smokers seen in an outpatient pneumological clinic. Two hundred eight smokers (group A) received medical advice and health care education with the offer of follow up. Seventy-seven smokers (group B) received the same BI protocol, with the offer of support treatment with nicotine gum (2 mg) and an explanation as to its use. One year after BI the patients were contacted by telephone to determine the number of non-smokers, with the result adjusted according to the truth index (71.4%) known for telephone response in this context. A total of 71 (24.9%) smokers were not located by telephone due to change of address, wrong number, exitus or lack of telephone. The estimated number of non-smokers in group A was 31.5/160 (19.7%) and 8.6/54 (15.9%) (non significant difference, chi square test). Group B's use of nicotine gum was therapeutically significant in 11.0% of the cases. We conclude that the efficacy of BI in the outpatient pneumological clinic is high.(ABSTRACT TRUNCATED AT 250 WORDS)