The infrared diode laser absorption spectrum of the fundamental band of the boron monoxide (BO) radical in its ground (2)Sigma (+) state has been observed. The source of the radical was the reaction of BCl3 with (OP)-P-3 in the absence of molecular oxygen. 15 lines of (BO)-B-11 and three lines of (BO)-B-10 have been measured. The (BO)-B-10 lines show a small, partially resolved, doublet structure of about 0.01 cm(-1) which is not present in the (BO)-B-11 species. This is attributed to the complex hyperfine pattern expected for the B-10 (I = 3) nucleus. The band origins are 1861.92465(48) and 1915.30554(16) cm(-1), respectively. Combining the diode laser value of B-t = 1.756829(11) cm(-1) with the microwave determination of B-o leads to a value of r(c) = 1.204068(7) Angstrom. for (BO)-B-11.