A simple roller bottle apparatus for growing B cell hybridomas in dialysis tubing yields high concentrations of monoclonal antibodies (Pannell and Milstein, J. Immunol. Methods (1992) 146, 43-48). Here we describe an adaptation of this apparatus for the simple production of high concentrations of the mouse macrophage specific growth factor, CSF-1. This apparatus appears to have general applicability for the production of other secreted cytokines.