A rapid method which does not require thinsectioning of Medicago sativa (alfalfa) nodules is described. Entire alfalfa nodules were initially stained by the DNA-specific Feulgen reaction and then the nodule tissues were cleared by a phenol treatment. This simple procedure allowed the visualization of the different developmental steps of nodule formation. Infection threads penetrating the inner root cortex, release of bacteria from the infection thread, meristematic nuclei and the formation of vascular bundles could be observed.