['To study the effect of nicardipine (Nic) on the cytoplasmic free calcium concentration ([Ca2+]i) in thymocytes and on the proliferation of thymus lymphocytes from mice in vitro.', 'The [Ca2+]i was measured by loading cells with the fluorescent dye Fura-2. The lymphocyte proliferation was determined by [3H] thymidine incorporation.', 'Nic 1-30 mumol . L-1 elevated [Ca2+]i of resting thymocytes with the percentages of its increase 43%-192% and 12%-148% in the presence and absence of extracellular Ca2+ respectively. Mitogen Con A 5 mg . L-1 also released Ca2+ from intracellular stores. Nic decreased the enhancement of [Ca2+]i induced by Con A. The IC50 (mumol . L-1) was 26.8 (95% limit: 24.8-29.0) and approximated to 10 in the presence and absence of extracellular Ca2+ respectively. Nic 1-30 mumol . L-1 did not stimulate the proliferation of resting lymphocytes from mouse thymuses (P > 0.05), but inhibited the proliferation when the lymphocytes had been stimulated by Con A (P < 0.01).'] Does nicardipine enhance cytoplasmic calcium concentration in mouse thymocytes in vitro?