The investigation of the protein composition of the different cell types of the ascidian Styela rustica blood cells have been done. Separation in discontinuous Percoll gradicnt shows 4 fractions. The 4th bottom fraction contains up to 100% of morula cells. The proteins composition of this fraction revealed on SDS-PAGF showed two major proteins with m.w. 47 and 26 kDa. Polyclonal antiserums AB26 and AB47 against these proteins have been raised. Each antiserum reacts with both proteins on the blot only in morula cells and stains the morula cells on parafin sections. Morula cells take part in tunic formation and reparation and in the defense reactions. In ovary AB26 and AB47 stain test cells which surround oocytes. Possible similarity of morula and test cells functions are discussed.