The bulb of Corydalis decumbens (Thunb) Pers, known as "Xiatian wu", has been used in Chinese traditional medicine for the treatment of central nervous system diseases. Many alkaloids have already been isolated from this herb (1). Further chemical studies were carried out in our laboratory in order to provide information needed for quality control requirements. We report on the structure elucidation of two phthalideisoquinoline hemiacetals. Compound 1a is a new optical stereoisomer of (+)-humosine A (1b). Compound 2 was identified as (+)-egenine and is identical with (+)-decumbensine isolated from this plant previously (2).