This study compared the effects of nebulized versus subcutaneous morphine on the intensity of dyspnea in cancer patients. Patients with a resting dyspnea intensity > or =3 on a 0-10 scale (0=no dyspnea, 10=worst possible dyspnea) who received regular oral or parenteral opioids were included. On day 1, patients received either subcutaneous (SC) morphine plus nebulized placebo or nebulized morphine plus SC placebo. On day 2, a crossover was made. Dyspnea intensity, side effects, and blinded preference of treatment were assessed. Eleven patients completed the study. Dyspnea decreased from a median of 5 (range, 3-8) to 3 (range, 0-7) after SC morphine (P=0.025) and from 4 (range, 3-9) to 2 (range, 0-9) after nebulized morphine (P=0.007). There was no significant difference in dyspnea intensity between nebulized and subcutaneous morphine at 60 minutes. Unfortunately, due to limited sample size, there was insufficient power to rule out a significant difference between both routes of administration. Nebulized morphine offered dyspnea relief similar to that of SC morphine. Larger randomized controlled trials in patients with both continuous dyspnea and earlier stages of dyspnea are justified.