The bronchodilatory effect of Neo-Biphyllin Mikroklysma® (400 mg Theophylline [T], 600 mg Diprophylline [D], 600 mg Proxyphylline [P], corresponding to 5.2 mg/kg bodyweight of T, and 7.8 mg/kg of D and P, respectively) was studied on 5 consecutive days with one daily rectal application in a double-blind crossover design in 8 patients with chronic obstructive lung disease. Serum levels following rectal application are lower than after oral administration. On the 5th day they are only slightly higher than on the 1st day. The mean serum levels (μg/ml) achieved after 2 h are 6.1 for T, 1.0 for D and 7.7 for P, after 8 h 3.5 for T, 0.9 for D and 4.8 for P. The pulmonary function parameters (FEV1, VC, RV, TLC and Raw) show an improvement, however, in comparison with placebo the results are statistically not significant. A correlation between the serum levels and the functional improvement cannot be established, even after taking into consideration the equipotency on a weight-for-weight basis according to the in vitro effect of the three compounds on the isolated guinea pig trachea [Boardman, 1980]. No side effects or local intolerance were reported. The use of the combination enema is particularly suitable for children or self-application by adults. Yet according to our findings larger doses or more frequent applications are require