An isolation procedure for functionally active lamina propria lymphoid cells (LPL) from the murine intestine is described. The procedure involved EDTA-dithiothreitol incubation of intestinal tissue to remove epithelial and intraepithelial cells, followed by collagenase digestion of the basement membrane to liberate part of the LPL. The LPL were suspended by squeezing the remaining tissue strips through a nylon gauze filter. Functional activity was tested by enumeration of the immunoglobulin-secreting cells in the cell suspensions obtained by an isotype-specific protein A plaque-forming cell assay. On average 1-2 X 10(8) LPL were isolated from the intestine of C3H/He mice. 11% of these cells actively secreted Ig. From these Ig-secreting cells 99% produced IgA. The isolation procedure described in this paper permitted a higher recovery of viable cells than has previously been obtained with other methods.