From an analog system K, digital systems Kd and Kbt are often obtained via the step-invariant and bilinear transformations, respectively. For the case when K is stable, it is shown that under certain conditions, Kbt converges to Kd in `p-induced norms as the sampling period tends to zero for 1 6 p 6 . Furthermore, Kbt converges to Kd in the graph metric as the sampling period tends to zero no matter whether K is stable or not. ? 2003 Elsevier Ltd. All rights reserved.