In some measles virus strains protein synthesis is restricted or reduced at higher temperature incubation. But in wild-type Buk strain and L-16 vaccine strain no changes in viral protein synthesis at 40 degrees C were shown. Radiolabelled Buk and L-16 proteins were precipitated with reconvalescent sera, vaccinated children's sera, subacute sclerosing panencephalitis patients' sera and rabbit antisera. There are no differences in the autoradiograms. However, antigenic variations in Buk strain proteins were discovered by using mAbs in radioimmunoprecipitation analysis. Buk strain hemagglutinin (H protein) has low binding ability in epitopes II and III in comparison with L-16 strain. Analogous changes were found in the epitope II of Buk strain phosphoprotein. Nucleocapsid, fusion and membrane proteins of the two strains have the same interactions with mAbs. In order to investigate H protein affinity with antihemagglutinins and receptors for erythrocytes a modified test for HA-inhibiting antibodies was used. But incubation time for sera and tween-ether antigens was varied from 0 min to 1.5 h. In "0 min" incubation time hemagglutinin can bind with antihemagglutinins or receptors for erythrocytes. But H protein binds more readily with antibodies. Buk strain H protein revealed antihemagglutinins in higher titers than L-16 strain antigen.