Reproduction of the vaccine L-3 strains of mumps virus was studied in cultures of continuous Vero cells and in primary cultures of Japanese quail embryos (JQE) growing on DEAE-Sephadex A-50 microcarriers. The Vero cell culture multiplies actively on the microcarrier surface giving more than a 20-fold increase in 8 days. Mumps virus showed a high reproductive capacity in Vero cell culture and in primary JQE cells. Mumps virus-infected Vero cells produce 5-6 pools of virus-containing material with a mean infectious titre 8.2-8.3 lg HAE50/ml. The primary JQE culture infected with mumps virus can yield 2-3 pools of virus-containing material. The intensity of mumps virus replication in the latter directly depends on the multiplicity of infection. Hemadsorption test could be performed in mumps virus-infected cell cultures on microcarriers.