The curvelinear correlations between the total testosterone levels and fluid intelligence in men and women

The relationship between serum total testosterone (T) level and the fluid intelligence (Cattell's Culture Fair Intelligence Test) was studied in men and women. There was no significant difference between IQs of men and women. There was an inverse curvelinear relationship between IQ and T in women. The same was found also in men, but the declining part of the regression line at high T levels was not as pronounced as in women. It is concluded that T may be related to IQ, even in subjects exhibiting no sex difference in IQ tests; too low or too high T levels may be disadvantages for the fluid intelligence, especially in women.