The automated flow cytometry system (FCM) at Memorial Sloan-Kettering Cancer Center has been used to monitor the effect of intravesical BCG in the therapy of superficial bladder cancer. Analysis of saline bladder washings prior to therapy, weekly during the six weeks of therapy, and at follow-up examination in 2 patients, 1 responder and 1 nonresponder, provides the basis for some projections regarding the potential value of this technique.