Preliminary studies with Mary Short, Ph.D. Children's Hospital Medical Center, Hematology/ Oncology Division, Cincinnati, OH 45229 This project is an attempt to evaluate the use of a fusion protein, consisting of enhanced GFP (uv) molecularly conjugated to an antibody directed at the GMCSF hematopoietic growth factor receptor, as a probe for flow cytometry. Various cell samples (controls and Spurlock cells) are prepared in Cincinnati and shipped to Los Alamos where we use the 406 nm liine from the krypton-ion laser on the 3-laser cytometer to excite the uv excitable GFP (maximum exicitation wavelength - 395 nm). In preliminary experiments we can easily detect the GFP fluorescence and in ongoing studies we will determine the optimal probe concentration and evaluate the fusion protein on other normal and tumor cell types. The end point would be to develop a sensitive, non-radioactive, assay for the GMCSF receptor.