A facile method has been developed for the highly sensitive and selective determination of ultratrace Be(II) ion using a new fluorimetric reagent, 10-hydroxybenzo[h]quinoline-7-sulfonate (HBQS), under extremely alkaline conditions, at pH 12.0. This reagent is quite suitable for the very small ion, Be(II), to form a 6-membered chelate ring, compatible with a high fluorescence yield. The stoichiometry of the chelate is 1:1 for Be-HBQS at pH 12.0. The calibration graph gave a wide linear dynamic range, 2-100 nmol dm(-3) of Be(II) ion with the detection limit (3s blank) of 0.52 nmol dm(-3), or 4.7 pg cm(-3). The excellent sensitivity and toughness toward the matrix influence were demonstrated using the artificial sample solutions for air-dust. Coupled with the simple masking procedure using EDTA, the method enables one to determine Be(II) ion at nanomolar levels in the presence of metals at the natural abundance levels in air-dust samples, typically Al, Ca, Cu, Fe, Mg, Pb, and Zn at 130, 150, 1.0, 70, 33, 3.0, and 8.0 micromol dm(-3), respectively, in the final solution. The proposed method was successfully applied to the determination of Be in urban air.