Most peptide hormone assays measure only fully processed bioactive peptides. Such assays are unsuited to detect hormone gene expression by alternative or attenuated prohormone processing (tissue- or cell-specific processing). The gastrin system is expressed in several different tissues and is therefore useful for studies of tissue-specific processing. Consequently we have developed a simple processing-independent radioimmunoanalysis for progastrin. Using antisera against the NH 2-terminus of a sequence, devoid of processing sites (preprogastrin 76–86) after trypsination of neighboring cleavage sites, the assay quantitates the mRNA product irrespective of degree of processing. Used together with a conventional assay for the mature carboxyamidated gastrins, the processing-independent analysis shows that in different tissues only 1 to 55% of the total translation product is processed to bioactive gastrins. Thus processing-independent analysis greatly improves the detection of gastrin gene expression at the peptide level. The principle of the assay should be applicable to all protein and peptide systems.