AbstractThe effects of calcium ions and of the calcium channel blockers verapamil, diltiazem and nifedipine on galvanotaxis inChlamydomonashave been investigated using a fully automated and computerized population system. Galvanotaxis is a function of the voltage applied to the cell population. However, the galvanotactic orientation also depends on the external calcium concentration. In a calcium‐deprived nutrient medium which still contains 6 × 10−7M calcium, galvanotactic orientation is about 20% of orientation at optimal calcium concentration of 10−4M at 9 V. The higher the external calcium concentration is, the lower is the voltage necessary for optimal galvanotactic orientation. The calcium channel blockers diltiazem and nifedipine likewise inhibit galvanotaxis ofChlamydomonasvery specifically without impairing motility. Verapamil is effective, but also inhibits motility by causing detachment or shortening of the flagella. Nevertheless, inhibition of galvanotaxis by verapamil is not the only result of decreased motility, because the galvanotactic orientation is impaired to a greater extent than motility. The effectiveness of the three blockers tested in inhibiting galvanotaxis depends on the concentration and on the voltage applied. At 10−5M, verapamil causes maximal inhibition of galvanotaxis at 9 V. At increasing concentrations up to 10−4M, diltiazem inhibits galvanotaxis more strongly than the other blockers. If the voltage is varied at a constant blocker concentration of 2 × 10−5M, nifedipine causes maximal inhibition at 3 V–6 V, diltiazem at 9 V and verap