The objective of this experiment was to test the possibilities of measuring the rate of DNA synthesis in chicken embryos by applying a simple 15 N tracer technique. We hypothesized that the rate of 15 N incorporation into liver DNA depends on the type of labelled substance, reflecting precursor availability to provide substrates for nucleotide synthesis. Fertilized eggs were divided into 4 groups (4 × 15): control -not treated, and treated with 15 N labeled glycine, ammonium chloride, or sodium nitrate. 15N labeled solutions were given in ovo by injection into albumen. After 20 days of incubation, the labeled substances had no effect on embryo development or morphology. Hepatic DNA was purified and 15 N abundance was measured by isotope ratio mass spectrometry. There was significant enrichment of 15 N in DNA from the glycine and ammonium chloride groups. We conclude that this simple technique of injecting 15 N tracers into incubating eggs can be used to estimate the rate of DNA synthesis.