Process for making a tow pre-preg comprising long continuous fibers coated with a thermoplastic polymer. A continuously moving spread tow of long continuous fibers, preferably carbon or glass, is humidified in an atmosphere of essentially 100% relative humidity and coated with particles of a thermoplastic polymer. A polymer particle-laden air stream contacts the moistened continuously moving tow, depositing polymer particles on the fibers. The fiber diameter is about 5-50 microns and the mean particle diameter is about 0.1-40 microns. The fibers with thermoplastic particles clinging thereto are continuously heated to a temperature sufficient to cause fusion of the thermoplastic polymer. This results in long continuous fibers coated with the thermoplastic polymer. The resulting tow-preg, or tow of coated fibers, is useful in the preparation of structural composites in which the fibers service reinforcing fibers. The thermoplastic coating polymer is a high performance polymer, such as polyether-ether ketone (PEEK), where high performance and the structural composite is desired. Polymer coating weights may vary from about 20% to about 90% of the total tow-preg weight.