A laboratory study was designed in order to investigate the effects of ventilation noise on performance, fatigue and annoyance. The study was also designed in order to compare the effects of broadband noise 40 dB(A), tonal noise, 40 dB(A), and tonal noise masked by means of low frequency pink noise, 41 dB(A). The study of performance was based on a figure identification test. The annoyance and fatigue were tested by means of rating scales. The analyses of fatigue also included EEG-recordings. The acceptability of the different types of ventilation noise was also analysed through matching tests. The differences in performance between broadband and tonal ventilation noise were significant and did not show any unambiguous tendency. An insignificant tendency of worse performance during broadband exposure and that the tonal ventilation noise should be more tiring could be observed. The tonal exposure was described as less annoying during work. On the other hand, in the matching tests, the subjects tolerated an insignificantly lower level of the tonal ventilation noise compared to the broadband noise. Comparisons between the tonal ventilation noise and the tonal ventilation noise masked by means of a pink noise, showed that the masked ventilation noise was correlated to ambiguous tendencies towards higher performance, lower fatigue but higher annoyance. In the matching tests, the subjects tolerated a lower level of masked ventilation noise compared to the unmasked ventilation noise. Except for the ratings of fatigue, all differences were below the level of significance p 0.05.