By studying 516 healthy adults normal reference intervals were established for the Coulter "S" haematological indices with the plasma ferritin, B12, folate and red cell folate in a subgroup of 306. Significant sex related differences were found for all measurements other than MCV, MCH and B12. After allowing for these sex related differences, the effects of age, body size, fasting, smoking, alcohol, exercise and contraceptive pill usage on the parameters studied was defined.