A human subject experiment was performed to examine the effect of office noise and temperature on human perception, comfort and office work performance. The experiment concerned offices of two different sizes with three different acoustical treatments. An open-plan office environment was simulated by playing office sounds through a surround-sound speaker system. The sound background was created by the ODEON room acoustic simulation software: I) a real open-plan office; II) an office as (I) but with a reflective ceiling; and III) an office as (I) but with the addition of acoustically absorbent surfaces. A cellular office environment was created by no sound being played. Subjects experienced all office environments at a comfortable temperature of 23°C and in the case of the cellular office and open-plan office (I) they experienced a second exposure at 28°C. A total of 15 subjects were exposed to the conditions and each exposure lasted for 6 hours. The presence of office noise and the type of office environment were found to have a significant effect on office work tasks that involved processing words. Results indicate that an excessive noise absorption in open-plan offices may have a negative impact on occupants’ perception of noise, the acceptability of noise and the performance of office work.