The minimal erythema doses (MED) to UVB and UVA radiation were measured in 254 normal subjects. Bivariate correlation analysis applied to the data showed a strong positive correlation between the UVB and UVA MEDs. By calculating the probability that a given combination of UVB and UVA MEDs is likely to occur in normal subjects, it was shown that, in some instances, both the UVB MED and UVA MED observed in a given subject may be within their respective normal ranges, but that the particular combination is more in keeping with abnormal photosensitivity.