We used reversed-phase high performance liquid chromatography (HPLC) to analyze the amounts of daidzein and genistein, well-known isoflavonoid aglycones, in methanolic extracts (80%) prepared from soy sprouts and also two types of soybeans (Soja hispida L.), one purchased at the local market and the other one cultivated in Turkey. Some commercially sold preparations containing either soy extract or soy isoflavones were also analyzed by HPLC for their daidzein and genistein content. Three oils obtained from the same soybean and soy sprout samples were analyzed for fatty acids by capillary gas chromatography-mass spectrometry (GC-MS). Several in vitro biological activities of the soybean oils were examined, including anticholinesterase, antioxidant, antibacterial, antifungal and antiviral activity. The soy sprouts were much richer in genistein (232.1 mu g/g) and daidzein (177.0 mu g/g) than the soybean samples. The cultivated soybean sample also showed higher genistein (3.771 mu g/g) and daidzein (3.366 mu g/g) levels than the soybean sample of market origin (2.971 mu g/g and 2.579 mu g/g, respectively). The soybean oils were found to be quite rich in essential fatty acids, and the soy sprout oil also contained essential fatty acids in appreciable amounts. The soybean oil of market origin had a notable antiviral effect against Herpes simplex as well as antifungal activity against Candida albicans at 8 mu g/ml.