Nanofibers were generated by melt blowing three sets of polymer blends, each comprised of pairs of immiscible components. Blends containing minority phases (25% by volume) of poly(ethylene--chlorotrifluoroethylene) (PECTFE) in poly(butylene terephthalate) (PBT), PECTFE in poly(styrene) (PS), and PBT in PS were dispersed as droplets in a continuous majority phase and melt blown into long (>100 μm) fibers with average diameters of several micrometers. Electron microscopy experiments revealed that melt blowing transformed the initial spherical dispersions into a nanofiber-in-fiber morphology. Macroscopic mats of nonwoven PBT and PECTFE nanofibers, with average diameters as small as 70 nm, were isolated by selectively removing the majority phase with a solvent. This method provides a potentially inexpensive, high throughput, one-step route to scalable quantities of polymeric nanofibers.