We report a mass spectrometric study of boron cluster anions (B-n(-), n = 7-55) produced by laser vaporization from two different types of boron-containing sample rods, one composed of YB66 and the other, pure boron. In mass spectra recorded from the YB66 sample, we observed a repeating intensity pattern of boron cluster anions having local maxima at (B-13(-))(B-12)(0,2,3) as well as at B-26(-). Similar phenomena were not observed with a pure boron sample. We attribute these observations to the structural differences between the two materials, and in particular to the (B-12)(B-12)(12) super-icosahedral structure of crystalline YB66. (C) 2003 Elsevier B.V. All rights reserved.