The authors present an automatic technic of estimation of ten serum proteins (albumin, alpha-antitrypsin, orosomucoid, alpha-1-macroglobulin, haptoglobin, C'3 complement, transferrin, IgM, IgG, IgA) by immunoopacimetry on a Centrifichem centrifugal analyser. This technic is derived from an immunonephelometric method, with the following differences: --the use of two concentrations of polyethylene glycol permitting one to obtain for all proteins, a constant levelling-out of the reaction within 3 minutes; --by a first reading at 3 seconds avoiding the prior determination of blank reagents and sera; --by the use of two dilutions of serum permitting calculation of all concentrations. The results are reproducible and are satisfactory: 95% of the coefficients of variation are less than +/- 5% in the case of all the proteins. The correlation with IDR is good. The coefficients vary from 0.91 to 0.99.