Heterogeneity of the residual variances was investigated for test day milk yields of Turkish Holsteins. A third order random regression model including the fixed, random additive genetic, permanent environmental and residual effects were used. Residual Variances (RV) of test day milk yields divided into different classes with 5 schemes as RV1, RV3, RV5, RV7 and RV10. Also, a structural model was fitted to residual variances of milk yields. The residual variances were estimated from 2.19-29.47 kg(2) and additive genetic variances were estimated 3.19-10.97 kg(2). The heritability estimates ranged from 0.12-0.81. The third order random regression models with RV7 and RV 10 schemes were found to be better than others for evaluation of residual variances.