90 schoolchildren aged twelve and thirteen years kept a dietary diary for three days. In most cases the average intake of vitamins was close to the recommended daily allowance, although for a minority the intake was low; with minerals the recommended daily allowance was less commonly achieved. To examine the possibility that deficiency of dietary minerals and vitamins was preventing optimum psychological function, a multivitamin/mineral supplement or a placebo was administered double-blind for eight months to 60 of the children. The supplement group, but not the placebo group or the remaining 30 who took no tablets, showed a significant increase in non-verbal intelligence.