This paper records the treatment of out-patients with chronic asthma by prednisolone administered in short courses and for continuous periods up to four years. A comparison of the effects of prednisolone with some of the newer steroid derivatives is also made. Assessment was made by comparing (1) the number of attacks of asthma, (2) the quantity of symptomatic drugs employed as spray or tablet, (3) the number of asthma-free days, and (4) the patient's own preference. When prednisolone was compared with bronchodilators (aminophylline or methoxyphenamine) it was found that 19 of the 26 patients had fewer attacks during the week on prednisolone,* four had more attacks, and three had the same number. Fourteen used a smaller amount of other symptomatic remedies while taking prednisolone, eight used more, and four used the same. Comparison of prednisolone with the dummy tablets showed that 17 had fewer attacks on prednisolone,* three more, and six the same; while 19 used smaller quantities of symptomatic remedies while on prednisolone, four used more, and three the same. For the total number of patients (26) 58 asthma-free days were recorded on prednisolone, 29 on bronchodilator tablets, and 26 on dummy tablets. Of 20 patients who expressed a preference, 16 favoured prednisolone.There appears to be little doubt that prednisolone given in this way can be effective in controlling asthma of moderate severity in a high proportion of patients. It was noticeable that while patients were on prednisolone, asthma-free days were usually recorded in the second half of the week.