We describe a group of basic isoforms of Par o 1 (cumulatively referred to as Par o 1b), purified by anion-exchange chromatography. The allergenic activity of Par o 1b was compared with that of the acidic isoform (Par o 1a) by RAST inhibition. Par o 1b showed a cathodic mobility in crossed immunoelectrophoresis. It was found to be homogeneous in SDS-PAGE and SE-HPLC (14.5 kDa), and heterogeneous in PAG-IEF, yielding five IgE-binding bands with pI ranging between 7.9 and 9.6 PAG-IEF individual components were isolated by cation-exchange HPLC. The N-terminal amino acid sequence of the main component (pI 8.8) was determined and found to be similar to that of Par o 1a.