Multilayer cultures of neonatal rat aortic smooth muscle cells, which were actively synthesizing elastin, were exposed to gamma-radiation. Elastin synthesis and accumulation was measured as a function of time after irradiation and compared to control (non-irradiated) cultures. Cells exposed to 50 Gy ceased to divide but continued to synthesize and accumulate elastin. The culture morphology suggested that the irradiated cells accumulated an extensive extracellular matrix between their cell layers. Interestingly, the amount of elastin accumulated in the irradiated cultures was nearly the same as in the controls despite the difference in cell number in the two cultures. Thus, on a per cell basis, the elastin accumulation was greater in the irradiated cultures than in the controls.