In order to seek a macrophage-activating substance, lipopolysaccharide (LPS) of plant origin other than that of wheat flour was surveyed. A large amount of LPS (10-100 micrograms/g) was detected in Laminaria japonica (kelp), Curcuma longa (turmeric), Undaria pinnatifida and other substances. Since concomitant bacteria possibly existing in root of farm products can be considered to contribute to LPS of plant origin, a count was taken of bacterial cells both dead and alive. This count revealed that some LPS were derived from concomitant bacteria which had probably come from root. Few concomitant bacterial cells were found in seaweed, while stem-root contained enough bacterial cells. Three predominant bacteria have been isolated and identified; Pantoea agglomerans, Enterobacter cloacae, and Serratia ficaria. These LPSs were purified and their chemical compositions were examined. They are similar to that of Escherichia coli except that their molecular sizes are smaller. Since LPS is non-toxic when taken orally or percutaneously, these LPSs may also be advantageous in the cure of intractable diseases.