Abstract: Immunoassay methods and apparatus are provided which utilize flow cytometry, coated latex microspheres, and labelled antibodies, to simultaneously detect the presence and amount of several antigens or antibodies in a sample. Microspheres can be sized by forward angle light scatter (FALS) or electronic volume. By combining FALS and fluorescence, it is practical to use beads of several different sizes, colors or shapes, each bead coated with a different protein or antibody, for the simultaneous detection of multiple analytes in a sample. Available auto-sampling systems make it even more appealing in this regard. In accordance with one embodiment, highly purified RNP. Sm, SS-A, SS-B and Scl-70 antigens are bound to 4, 5, 6, 7 and 10 .mu.m latex beads, respectively and stabilized for extended shelflife. Diluted patient serum is placed into test tubes containing a mixture of the five antigen coated beads and incubated. If an antibody is present for a specific antigen, it will bind to that specific bead.