In the paper four types of estimations of the linear function of the variance components are presented for the mixed linear model $𝐘=𝐗\beta +𝐞$ with expectation $E\left(𝐘\right)=𝐗\beta$ and covariance matrix $D\left(𝐘\right)={\mathbf{0}}_{\mathbf{1}}{𝐕}_{\mathbf{1}}+...+{\mathbf{0}}_{𝐦}{𝐕}_{𝐦}$.