Several flagellar dynein ATPase and radial spokehead genes have been isolated from a Chlamydomonas genomic expression library in lambda gt11. The library was probed with polyclonal and monoclonal antibodies raised against purified flagellar polypeptides, and recombinant phage giving positive signals were cloned. In vitro translation of mRNAs hybrid-selected by the cloned sequences from whole cell RNA provided confirmation of identity for three of the four clones. Evidence supporting the identification of the fourth, which encodes a dynein heavy chain, was provided by antibody selection; the fusion protein produced by this clone selected heavy chain-specific antibodies from a complex polyclonal antiserum recognizing many dynein determinants. One of the radial spoke sequences isolated here is of particular interest because it encodes the wild-type allele of a locus which was defined previously by temperature-sensitive paralyzed flagella mutation pf-26ts (Huang, B., G. Piperno, Z. Ramanis, and D. J. L. Luck, 1981, J. Cell Biol., 88:80-88). The cloned sequence was used to hybrid-select mRNA from mutant pf-26ts cells, and when translated in vitro, the selected mRNA produced a mutant spokehead polypeptide with an altered electrophoretic mobility. This confirms that the pf-26ts mutation alters the primary structure of a radial spokehead polypeptide. To quantify spokehead and dynein mRNAs during flagellar regeneration, all of the cloned sequences were used as hybridization probes in RNA dot experiments. Levels increased rapidly and coordinately after deflagellation, peaked 3-10-fold above nondeflagellated controls, and then returned to control values within 2 h. This accumulation pattern was similar to that of flagellar alpha-tubulin mRNA.