The adaptation to extreme concentrations of Ca 2+ and its consequence on the properties of the 45 Ca 2+ transport were studied in submerged mycelia of Trichoderma viride. The adaptation to low [Ca 2+ ] o did not cause changes in kinetic parameters of the 45 Ca 2+ influx but the adaptation to high [Ca 2+ ] o increased the K M(Ca2+) . The V max of the 45 Ca 2+ influx decreased with the age of (non-adapted) mycelia with concomitant decrease of the K M(Ca2+) these changes were prevented in mycelia adapted to high Ca 2+ . High [Ca 2+ ] o decreased the stimulation by the uncoupler, 3, 3′, 4′, 5-tetrachloro salicylanilide (TCS) (30 μM), as compared to the control, whereas the Ca 2+ chelator, EGTA, stimulated it. In the aged mycelia, the stimulation by TCS of the 45 Ca 2+ influx faded away, in parallel with the activity of the H + -ATPase. The 45 Ca 2+ efflux from mycelia was affected by TCS in a similar way as the 45 Ca 2+ influx. The results demonstrate the adaptive responses of transport processes participating in the mycelial Ca 2+ homeostasis and ageing are in agreement with a notion that both Ca 2+ -influx and-efflux are coupled by the H + -homeostasis at the plasma membrane.