Uncleaved eggs, eggs with 4, 32-64 blastomeres and blastulae were irradiated with different doses of UV-mixed light, only onesided-equatorial, -animal or -vegetativ. In no case did the UV-irradiation effect a statistically significant increase of whole or partial visceral inversions. These happened only after irradiation of young gastrulae, especially when the vegetative germ part with the blastopore was exposed.