The diode laser absorption spectrum of the nu(13) band of benzene cooled in a supersonic expansion has been recorded with the help of a multipass optical system built inside the vacuum chamber. Transitions from low J, K values (0-10) are reported for the first time for this band. The observed frequencies agree with the ones computed with previously existing spectroscopic constants. The rotational temperature of the expansion has been evaluated to be 8 +/- 5 K when using He as buffer gas at a stagnation pressure of 1.5 bar. This value lowers in 1:10 mixtures of Ar:He at the same pressure. The effect of the carrier gas on the linewidth is also discussed. Copyright 1999 Academic Press.