Production lines with integral control limits are studied in this paper. The behaviour of such lines can be shown to be approximated by that of flow lines with local buffers. The reduction of an integrally controlled line to a locally controlled one is computationally simple and accurate in the estimation of such performance measures as throughput, probabilities of buffers being full or empty and throughput time. The advantage of such a reduction is that good techniques are available for estimating the performance of flow lines with local buffers only. Furthermore, a direct method is described for obtaining an estimate of the throughput of lines with integrally controlled buffers only. In the model used here, the product flow is continuous and the production units are unreliable. Both lifetimes and repair times of machines are distributed exponentially.