Experiments were conducted to test for ricin content in tissue samples from four castor cultivars, developing castor seed, germinating castor seedlings, and chemically and heat treated seed meal. Ricin content of each sample was examined via Western blotting with ricin A-chain specific antibodies. Results indicate that ricin is present solely within castor endosperm and is not present any other tissues. Samples from developing seed and germinating seedlings indicate ricin production begins around day 28 post pollination, and ricin is absent from the seedling 6 days after the onset of radicle emergence. This would seem to indicate that the purpose of ricin is to protect the seed and not the entire plant. Ricin content of seed meal treated separately with heat and chemicals was tested. It was found that hot-pressing of the seed was sufficient to denature ricin in the seed meal.