Several odorant-binding proteins (OBP) have been previously purified from the nasal mucosa of the old world porcupine Hystrix cristata. In this paper, we report their N-terminal amino-acid sequences and accurate molecular weights, as measured by electrospray mass spectrometry. The partial amino acid sequences reveal significant similarity with OBPs of other mammalian species and segregate the eight proteins purified into two subclasses. Mass spectrometry has revealed microheterogeneity among the proteins belonging to each of these two groups, suggesting a total number of OBPs of at least nine. The molecular weight differences between OBPs cannot be readily accounted for by common post-translation modifications and indicate different gene products. Such a large number of different OBPs may represent further support to an odour discriminating role for these proteins.