Several endocrine tumor markers are routinely used in the diagnosis and management of various cancers. The current assays, however, typically take several hours to perform, which precludes their use in the intraoperative management of patients. Most endocrine tumor markers have a half-life in the circulation of less than 5 minutes, thus making it feasible, if a rapid assay were available, for monitoring the concentration of the hormones during surgery or localization procedures. The primary indication for such assays would be to assess the extent of residual tumor after surgery and to localize tumors by selective venous or arterial sampling. In the past year, we have improved the assay for PTH by using antibodies specific for the intact protein. We also have modified an existing commercial assay for gastrin for developing a rapid immunoassay. In the upcoming year, we plan to further develop the gastrin assay and to assess its potential clinical utility on patient specimens.