A 9 kDa basic protein called Probable Amylase/Protease Inhibitor (PAPI) was purified from rice seeds and its complete amino acid sequence was determined[Yu et al. (1988) Arch. Biochem. Biophys. 265, 466-475]. Recently its amino acid squence was found to be similar to those of phospholipid transfer proteins [Bernard and Somerville (1989) Arch. Biochem. Biophys. 269, 695-697]. During the purification of PAPI from rice seeds, other basic proteins of molecular masses smaller than 15 kDa have been isolated. One of them is another 9 kDa basic protein, very similar to the previously characterized rice PAPI. Partial sequencing of the newly isolated 9 kDa protein shows that its sequence is almost identical to that of rice PAPI. Therefore, the two proteins are called PAPI-A (previous study) and PAPI-B (present study), respectively. The numbers of lysine and cysteine residues in the PAPI-B protein, determined by the electrophoretic method of Creighton, were found to be the same as in PAPI-A. The PAPI-B protein did not show any inhibitory activities against various amylases and proteases tested so far.