Calcium administration in vivo enhances activation of peripheral T cells. Hypercalcaemia in mice was induced by daily intraperitoneal injection of calcium gluconate (2000 mg/kg/day) starting 3 days before immunization. Total calcium (A) and total sodium (B) in serum were quantified on an ARCHITECT c16000 analyser 22 days post-immunization (representative plots of two independent experiments; data given as mean ± SEM; n = 6–7). Inguinal lymph node cells (C) and splenocytes (D) were isolated and analysed for T-cell activation by FACS 22 days post-immunization (representative plots of two independent experiments; data given as median; n = 7–9).