Background : Clinical laboratories seeking accreditation for compliance with ISO 15189:2003 need to demonstrate that the physiological reference intervals communicated to all users of the laboratory service are appropriate for the patient population served and for the measurement systems used. In the case of immunological quantities, few articles have been published in peer-reviewed journals. Methods : A total of 21 clinical laboratories in different regions of Spain collaborated in identifying reference individuals and determining adult reference intervals for some immunological quantities measured using RD/Hitachi Modular Analytics analysers and Tina-Quant ® reagent systems. These immunological quantities are the mass concentrations of immunoglobulin A, immunoglobulin G, immunoglobulin M, complement C3c and complement C4 in serum. All the logistic work was carried out in co-operation with the supplier of the reagents and analysers (Roche Diagnostics España, S.L., Sant Cugat del Vallès, Catalonia, Spain). From the set of reference values obtained by each laboratory, multicentre reference limits were estimated non-parametrically. Results and conclusions : The reference intervals estimated in this study for concentrations of serum components under consideration are: complement C3c, 0,62–1,64 g/L for women and men; complement C4, 0,14–0,72 g/L for women and men; immunoglobulin A, 0,89–4,80 g/L for women and men; immunoglobulin G, 6,5–14,3 g/L for women and men; and immunoglobulin M, 0,48–3,38 g/L for women and 0,41–2,46 g/L for men. (According to ISO, IUPAC and IFCC recommendations, the comma is used as the decimal sign.) Clin Chem Lab Med 2007;45:387–90.