We present the results of a study designed to verify the efficacy of nebulized L-Adrenaline and/or dexamethasone given intramuscularly (IM) in the treatment of croup during childhood. Sixty-six children, hospitalized for croup during the period between october 1989 and september 1990, entered the study. They received the ordinary treatment with oxygen-therapy and fluid-therapy and were randomly assigned, in a double-blind fashion, into one of four treatment groups: Group 1: Nebulized L-Adrenaline and placebo (IM). Group 2: Nebulized saline and placebo (IM). Group 3: Nebulized saline and dexamethasone (IM). Group 4: Nebulized L-Adrenaline and dexamethasone (IM). The clinical evaluation was based on a scoring system assessing the inspiratory stridor, croupy cough, retractions and cyanosis. An analysis of variance was performed on the evolution of the score for two factors (Adrenaline and dexamethasone) to verify that there was no interaction between them. Subsequently, a one-factor analysis of variance was performed on the four treatment groups. We conclude that nebulized Adrenalin is more beneficial than saline in the clinical evolution of croup (p < 0.05). However, we did not find a statistically significant improvement in the group treated with dexamethasone when compared with the group treated with the placebo IM injection.