A 34 yr old heroin addict was referred because of chest pain caused by air-trapping in a bulla in the left lower lobe. There was a marked difference between the functional residual capacity measured by body-plethysmography and helium dilution. A slow wash-in and wash-out were demonstrated by ventilation scintigraphy with Xenon133. Bullous degeneration is a known complication of intravenous drug abuse. Usually these bullae are found in the upper lobes. Possible causative mechanisms are discussed.