Walter Nelson-Rees (January 11, 1929 – January 23, 2009) was a cell culture worker and cytogeneticist who helped expose the problem of cross-contamination of cell lines.

He used chromosome banding to show that many immortal cell lines, previously thought to be unique, were actually HeLa cell lines.

The HeLa cells had contaminated and overgrown the other cell lines.

In 2005 he received the Lifetime Achievement Award, from the Society for In Vitro Biology (SIVB).

[3] He died on January 23, 2009, in San Francisco, California, from complications from a broken hip.