Light absorption provides the basis for a fast and nondestructive method for determining concentrations of black carbon (BC). The laser transmission technique measures the attenuation (ATN) of visible light as it passes through filter samples. We have measured [BC] and ATN simultaneously for a large number of solvent-extracted source and ambient particle samples, using temperature-programmed evolved gas analysis with continuous light attenuation measurement. For all data with ATN ≤ 200, ATN is directly proportional to [BC], with the proportionality constant = 25.4 ± 1.7 cm 2 μg −1. Because the relationship between ATN and [BC] does not depend on the origin of the carbonaceous particles, measurement of ATN alone can provide a good estimate of the black carbon concentration.