SummaryStaphylococcal enterotoxin B (SEB) may be assayed by a simple and rapid latex-fixation test, with sensitivity improved by several orders of magnitude over conventional methods. Latex particles, coated with specific antitoxin under carefully controlled conditions, were exquisitely sensitive indicators of toxin. The minimal detection limit, 2 × 10-4 μg of SEB/ml of sample, equivalent to 1 × 10-5 μg/well in the assay plate, can apparently be extended to an even lower value with instrumented reading of end points. Titrations require only 100 μl of sample.