Patients experiencing dyspnoea can request an additional dose of salmeterol during the dose interval for the control of their symptoms, although under treatment with salmeterol. In this study we have explored the effects on respiratory function of an additive dose of salmeterol Diskus in 15 chronic obstructive pulmonary disease (COPD) patients in regular treatment with a conventional dose of 50 microg salmeterol. On two different days, patients inhaled 50 microg Diskus. After 240 min, they inhaled additional 50 microg salmeterol Diskus (salmeterol arm) or placebo Diskus (placebo arm). Lung function was controlled before first drug administration and 0.5, 1, 2, 3, 4, 4.5, 6, 8, 10, and 12 h thereafter. The mean (95% CI) peak increase in FEV1 from baseline was reached after 4 h in the salmeterol arm (0.174 L; 0.144-0204) and after 5 h (0.141 L; 0.115-0.168) inthe placebo arm; after 12 h, the mean (95% Cl) increase in FEV1 from basal values was still 0.149 L (0.119-0.179) in salmeterol arm, but only 0.041 L (0.017-0.064) in placebo arm. The mean (95% CI) FEV1 AUC0-12h for all patients were 2.01 (1.72-2.30) L when salmeterol was added and 1.30 (1.03-1.58) L when placebo was inhaled. The difference (mean; 95% CI) between the FEV1 AUC0-12h of the two arms (0.71 L; 0.47-0.95) was statistically significant (P<0.0001), although the difference (mean; 95% CI) between the FEV1 AUC0-4h of the two treatments (0.08 L; -0.02-0.18) was notstatistically significant (P=0.126). The addition of an extra dose of salmeterol did not significantly increase the heart rate or decrease the SpO2. This study suggests that the addition of an extra dose of salmeterol does not give room for further increase in peak FEV1, but the effect of adding salmeterol to salmeterol is largely additive when considering the duration of action and safe.