The sound power levels emitted by five vacuum cleaners and one reference sound source were determined in four different acoustic environments in accordance with appropriate domestic and international measurement standards, and also using only four measurement locations, to ascertain any differences between the various procedures. The study shows general agreement among the results, (rms differences between A-weighted sound power levels of 1.0 to 1.5 dB). Determinations conducted in the reverberation room appear systematically low by about 0.8 dB (A-weighted sound power level); determinations made using four microphones may be biased if the microphones are located too close to the source. Use of the comparison (reference sound source) method eliminated systematic bias and improved the agreement between environments (rms differences of 0.5 to 1.0 dB).