summary Utilizing the skin window technique, symmetry of cellular response was examined by comparing cellular exudates from symmetrical areas of opposite forearms in eleven subjects. Testing the hypothesis that there would be no significant difference between symmetrical sites subjected to the same stimulus at the same time, the percentages of cell types in the cellular exudate were calculated for 126 paired comparisons. A significant difference in the cell types arriving at the skin window sites occurred in seventy‐six out of the 126 paired comparisons (Chi square analysis, P<0.01). This lack of a symmetrical response could be due to an inherent variability of the cellular response or to an inability to manipulate the two sites in exactly the same manner. Although significant differences were found between the above individual matched pairs (Chi square analysis), the ‘t’ test analysis of the pairs grouped by hour revealed no significant difference in mean percentages of cell types between left and right arms at fourteen time intervals. Thus, previous skin window investigations comparing mean percentages of cell types were found to be valid, even though symmetry of cellular response in individual subjects is much less than expected.