AbstractCa2+has profound effects on the movement of cilia and eukaryotic flagella, including those of Chlamydomonas. Two clear changes seen in Chlamydomonas flagella with changes in Ca2+are beat frequency and symmetry. Photographic and computer assisted analysis of flagellar bending patterns on a uniflagellate mutant of Chlamydomonas have been used to examine details of the effects of Ca2+on the movement of ATP‐reactivated, demembranated flagella. In addition to the forward mode bending pattern seen at low Ca2+concentrations (10−9M), which has a frequency of about 50 Hz and the reverse mode bending pattern seen at high Ca2+concentrations (10−4M) with a frequency around 70 Hz, we carefully examined bending patterns in the intermediate Ca2+concentration range of 1–6.5 × 10−6M. In this intermediate range, the bending patterns have significantly reduced asymmetry and slightly increased frequency, compared to the motility observed at low Ca2+concentrations. These observations indicate that changes in these two parameters of motion do not occur in parallel and suggest that the effects of Ca2+may be a multicomponent process. Physiologically, these changes in the beat pattern at intermediate Ca2+may signal either (1) the beginning stages of transition to the symmetrical, high‐frequency beating seen at high Ca2+, or (2) a more normal forward mode motility for thetransflagellum as suggested by Kamiya and Witman [1984]. No large amplitude bending patterns associated with transitions between forward and reverse mode beating in intact cells were seen at the intermediate Ca2+co