This article describes methods to inject large numbers of echinoid eggs and zygotes with globin mRNA and label them with tritiated amino acids. The products can be quantitatively analyzed to determine the amounts of peptide synthesis. The injections can be performed quickly and require relatively simple and inexpensive equipment. Although I designed my methods to inject large numbers of echinoid eggs and zygotes, these methods should also be useful for injecting many different molecules and ions into smaller numbers of cells as well as into a variety of cell types.