Biological activities of the 50% ethanolic extract of Kijitsu, dried immature Citrus fruits prepared from C. hassaku Hort. ex Tanaka (H), C. natsudaidai Hayata (N) or allied plants (T, A) were observed. Weak toxicities, weak intestine or uterine relaxant activities, beta-adrenergic activities were shown by in vitro experiments and antiasthmatic activity by intraperitoneal administration. These activities among each extract did not differ. The content of flavonoids (narirutin, naringin hesperidin, neohesperidin) or synephrine did not show much difference among the four dried immature Citrus fruits. These results suggest that H can be used for medicine as the substitute for N, T or A which has been commonly used as Kijitsu. This method is generally applicable to the proof of the biological equivalency of the crude drug and its substitutes.