Human interleukin-2 (hIL-2) production in Escherichia coli and insect cell/baculovirus expression systems can be inefficient. Here a investigated secreted production of hIL-2 fused with green fluorescent protein (GFP) as a. versatile fusion partner in optimized stately transfected insect Drosophila melanogastsr S2 cells. This nonlytic S2 insect cell expression system employs a plasmid vector and allows for secretion of functional human proteins. We report that, following stable transfection and induction, S2 cells secreted hIL-2 as a fusion protein (similar to2.3 mug/mL yield), with a secretion efficiency of approximately 90%. Regression analysis indicated a single linear relationship existed between GFP fluorescence and hIL-2 mass in both whole cell and secreted medium samples, indicating that in viva monitoring anti quantification of met foreign protein expression and even secretion is possible using this system. The simple comparative measurement of FP fluorescence also allowed motoring of secretion. efficiency during periods of high GFP/hIL-2 expression.