1976: The first sperm injected into an egg
The Modern Laboratory · The Modern Papers
The Modern Papers · MP·01 · 1976
1976: The first sperm injected into an egg
In Hawaii, a needle carried a single sperm into a hamster egg, and the egg answered.
The story
Tsuyoshi Uehara, working in Ryuzo Yanagimachi's laboratory at the University of Hawaii, injected hamster sperm straight into hamster eggs. Inside the egg the sperm heads swelled and became male pronuclei, the first visible step of fertilisation. Human sperm, including sperm that had been frozen and thawed, did the same inside hamster eggs.
It was a laboratory question, not a treatment. Whether an injected egg could become a living animal was not shown in the mouse until 1995. But sixteen years after this paper, in Brussels, the same idea became ICSI, and a treatment for almost every kind of male infertility (FP·12).
Uehara worked with an upright microscope, so that every image he steered his needles by was upside down and reversed.
The paper
Microsurgical Injection of Spermatozoa into Hamster Eggs with Subsequent Transformation of Sperm Nuclei into Male Pronuclei
Tsuyoshi Uehara, Ryuzo Yanagimachi
Biology of Reproduction 1976;15(4):467 to 470. November 1976. Read the paper.
Find it in the museum
Room 2, One sperm, one egg, Tsuyoshi Uehara, Ryuzo Yanagimachi
How we know
Citation checked against PubMed (PMID 974199) on 14 October 2026. No abstract is indexed; the account follows the sources on our Uehara and Yanagimachi pages, including the Society for the Study of Reproduction's 2024 history of ICSI.
The IVF Museum · The Modern Papers
Compiled with AI-assisted research and checked against the original sources. Undergoing peer review. Corrections are warmly welcomed.
