We report here the first measurements of volcanic SO2 fluxes obtained on foot, using a miniature ultraviolet spectrometer. Our measurements, based on differential optical absorption spectroscopy (DOAS), were performed ≈1 km from the summit of Masaya volcano (Nicaragua) in December 2001, and yielded a mean SO2 emission rate of 4 kg s-1, comparable with a set of contemporaneous measurements obtained by road vehicle traverses (average 6 kg s-1). SO2 flux estimates (average 4 kg s-1) were also obtained from a fixed position by scanning the plume. This range of fluxes confirms an apparent decrease in gas output from the volcano since 2000. The portability and ease of use of the spectrometer offer considerable scope for routine measurements of SO2 emissions from volcanoes, especially where road access or opportunities for airborne campaigns are limited. These approaches can be readily extended to monitor other sources and gases.