Processing of fiber diffraction patterns is generally more difficult than for single-crystal patterns, and requires different algorithms and software. The program WCEN has been developed to determine experimental and specimen parameters and to convert diffraction data from detector to reciprocal space, and offers a variety of input and output formats, running under Mac OS X and Linux. The program is described and examples from oriented sols of filamentous plant viruses, illustrating different strategies for parameter determination and refinement, are given.