Like all computing platforms, grids are in need of a suite of benchmarks by which they can be evaluated, compared and characterized. As a first step towards this goal, we have developed a set of probes that exercise basic grid operations with the goal of measuring the performance and the performance variability of basic grid operations, as well as the failure rates of these operations. We present measurement data obtained by running our probes on a grid testbed that spans 5 clusters in 3 institutions. These measurements quantify compute times, network transfer times, and Globus middleware overhead. Our results help provide insight into the stability, robustness, and performance of our testbed, and lead us to make some recommendations for future grid development.