Abstract: Message RNA is immobilized directly from cells onto filter material. Immobilization is carried out by solubilizing cellular components with a chaotropic salt, passing the resultant solubilized cellular components through a filter which selectively binds message RNA and baking the filter containing bound message RNA. The chaotropic salt is preferably sodium iodide, potassium iodide or sodium perchlorate. Prior to solubilizing, the cells may be washed and lysed. The bound message RNA can be hybridized to a labeled probe and the amount of message RNA measured. Prior to baking, the filter containing bound RNA may be incubated in a solution which acelylates basic protein and other molecules which might interfere with molecular hybridization.