Temperature, humidity and nasal peak inspiratory flow rate (PIFR) are potential variables in the quantitative measurement of olfactory thresholds in the clinic. To date, these variables have not been properly evaluated with respect to olfactory perception, and therefore the aim of this study was to determine their effect on the thresholds. These variables were measured on 10 occasions in 10 subjects over a 10-week period. The results obtained were then subjected to statistical analysis using a linear mixed-effect model. This demonstrated that olfactory thresholds are sufficiently independent of room temperature, peak humidity and nasal PIFR in a routine outpatient clinic environment in normal subjects, with no evidence of any statistically significant influence by these variables.