This report deals with the general problem of estimating the incremental detection capability of a seismic station, i.e., the probability of detection as a function of event magnitude. A maximum likelihood procedure is introduced to estimate the station detection thresholds by comparison with an independent reference station or network. Approximate confidence limits for the estimated parameters are computed. The results obtained by this (direct) method are compared to estimates derived from applying the exponential magnitude- frequency relationship of natural seismicity. It is found that the latter (indirect) method in general gives significantly lower 90 percent detection thresholds. It is concluded that, if a good reference system is available, the direct method will produce estimates that are more reliable than those provided by the indirect method.