Two napins (nIa and nIb), isolated from Brassica napus (rapeseed) seeds, have been sequenced. The two proteins show the common structural pattern of the 2 S albumins, since they are composed of two disulfide-linked chains of different size, yet they exhibit an atypical low molecular weight (12.5 kDa vs. 14.5 kDa of the major napins). High sequence similarity has been found between these 2 proteins, but only 54% similarity can be estimated from their comparison with the 14.5 kDa major napins. Thus, nIa and nIb are considered representatives of a new distinct group of rapeseed napins since all the previously known napins exhibit 95% sequence similarity. Unexpectedly, the similarity increases when compared with the 2 S proteins from other species.