It has been demonstrated that conjunctive stimulation of cerebellar climbing fibres and parallel fibres induces a long-term depression (LTD) of the transmission from the activated parallel fibres to Purkinje cells. The aim of the present investigation with extracellular recordings from single Purkinje cells was to study factors influencing the induction of LTD. Climbing fibres and parallel fibres were conjunctively stimulated with a constant time interval between the climbing fibre and parallel fibre stimuli. It was demonstrated that the maximal effective time interval between climbing fibre and parallel fibre activation for induction of LTD was between 125 and 250 ms. It was also demonstrated that the amplitude of the LTD depended on the stimulation frequency. The LTD induced by conjunctive stimulation at 1 and 2 Hz had a similar size whereas the LTD induced by 4 Hz was stronger.