A new triterpene, tetramethylsqualene, produced by Botryococcus braunii var. showa, was isolated and characterized by NMR and mass spectroscopy. The compound is a squalene derivative with non-isoprenoid methyls at C-3, C-7, C-18, and C-22. Tetramethylsqualene was a minor component (ca 0.2%) of normal cultures; however, its concentration increased 20-fold in cultures supplemented with 2.1 mM L-methionine.