The individually different effects of exposure to comparable levels of chemicals might be partly explained by dissimilar response sensitivity towards chemicals. Multiple chemical sensitivity (MCS) might be the clinical endpoint of this altered sensitivity. Concerning a subclinical range of chemical sensitivity, 'challenge studies' with people reporting chemical sensitivity are needed to improve the knowledge about such differences. The chemical and general environmental sensitivity questionnaire (CGES) is a standardized screening tool for the selection of this group. In the present study 24 healthy male volunteers, half of them classified as sMCS-subjects, were experimentally exposed to 2-butanone and ethyl benzene at different levels (TLV-level vs. odor threshold). The strength of self-reported sensory irritations (nasal and ocular) and symptoms of bad smell were assessed, prior, during, and after the 4 hours of exposure. The time courses of sensory irritations were affected by sMCS. Across all exposure periods sMCS-subjects showed increasing symptom scores while control-subjects did not. Symptoms of bad smell were affected by three exposure-related factors (substance, level, duration) without any additional influence from the sMCS factor. Starting from these results it could be concluded that the time-depending influence of reported chemical sensitivity is most prominent for subjective data of sensory irritations.