A method, utilizing brine shrimp (Artemia salina LEACH), is proposed as a simple bioassay for natural product research. The procedure determines LC50 values in µg/ml of active compounds and extracts in the brine medium. Activities of a broad range of known active compounds are manifested as toxicity to the shrimp. Screening results with seed extracts of 41 species of Euphorbiaceae were compared with 9KB and 9PS cytotoxicities. The method is rapid, reliable, inexpensive, and convenient as an in-house general bioassay tool.