A conditional test is proposed that uses the null hypothesis of bivariate symmetry to detect unequal marginal scales in a bivariate population. The asymptotic normality of the test statistic and the consistency of the test are established. Asymptotic relative efficiency comparisons are made with the standard parametric test in both the bivariate normal case and in a trivariate reduction model case and with two of Sen's (1967) tests in the bivariate normal case. The good performance of the test is also illustrated via a Monte Carlo study.