Ultraviolet spectra of solutions of instant and filter coffees have been analysed as a linear combination of component Gaussian bands. We show that the ratio, R′, of two of these bands, one at 329 nm due almost entirely to chlorogenic acid, and the other at 272 nm due to a coffee component not appearing in the chlorogenic acid spectrum, is analogous to the ratio R (Hamboyan et al. 1989). The use of R which is easier to measure than R′ has therefore been justified on physical grounds, based on the existence of component spectral bands. Filter coffees appeared to exhibit behaviour similar to that of instant coffees.