The construction of a simple micro-injection device with a micrometer drive is described. The system was tested by injecting different volumes (0–75 nl) of 14C-protein hydrolysate into embryos of Xenopus laevis using 3 different micropipettes (tip diameters 5, 10 and 15 μm) followed by determination of the amounts of radioactivity in the embryos. Statistical analysis showed a perfect linear relationship between number of micrometer units and injected volume. This relationship was independent of the micropipette used, so that no precalibration is needed. The inaccuracy of the injected volume was in all cases less than 3%. As one out of many possible applications the apparatus was used to study the biosynthesis of soluble proteins in early embryos of Xenopus laevis.