Abstract A rapid, sensitive, and quantitative radioimmunoassay for specific translation products was developed using Escherichia coli cells grown in 96-well microtiter plates. A simple and inexpensive apparatus that facilitates the simultaneous transfer of all 96 detergent-lysed cultures to nitrocellulose within 30 s is described. Following this quantitative transfer, selected proteins are screened using specific antisera and 125I-Protein A. The technique works with either cytoplasmic or membrane proteins. As little as a two- to threefold increase of a gene product over normal levels can easily be detected.