The resonance lines in the spectrum of an element emitted by a hollow-cathode spectral lamp are selectively modulated by applying a pulsing technique which produces a pulsating cloud of atomic vapour inside the lamp. The vapour absorbs only the resonance lines and a unique modulation of the resonance lines is achieved. A simple atomic absorption spectrophotometer employing this method of resonance line modulation and not requiring a monochromator is described. Calibration curves for copper obtained using this instrument are presented. © 1969.