Continuous flow offers notable advantages over batch processing for analytical applications like gene expression profiling of biological material, which demands very high processing. The technology of choice for future genetic analyzers will most likely use the polymerase chain reaction (PCR); therefore, high-throughput, high-speed PCR devices have raised enormous interest. Continuous-flow, biphasic PCR can meet these requirements but segmenting∕carrier fluids chemically compatible with the PCR are needed. The present paper compares several fluids in terms of compatibility with PCR and fluidic dynamics in a continuous, two-phase flow microfluidic device, and PCR efficiency was assessed quantitatively. The results represent the first step toward rational fluid design for biphasic continuous PCR.