We have examined the structural proteins of Rauscher murine leukemia virus (R-MuLV) by means of rocket immunoelectrophoresis and crossed immunoelectrophoresis, using polyspecific antisera to Tween/ether-disrupted purified R-MuLV. Fifteen different precipitation lines were recognized in virus lysates. Using five reference antisera prepared to purified R-MuLV-structural proteins, the precipitation lines of p 10, p 15, p 30 and gp 69/70 were identified. These techniques, although less sensitive than radioimmunoassay, have several advantages, such as simplicity, direct control of precipitation reactions and possibility of using crude antigen preparations.