An unusual case of intravascular lymphomatosis caused by small noncleaved, non-Burkitt's lymphoma, which presented with adult respiratory distress syndrome, is described. Extensive invasion of the small- and medium-size blood vessels of the lung, liver, spleen, kidneys, heart, esophagus, stomach, small and large intestines, bladder, and brain-but not the bone marrow or peripheral blood-is documented. The possible mechanism and the unusual features of this case are discussed in comparison with previously reported cases. The pertinent literature is reviewed. The problem of diagnosing this pathological entity is emphasized.