William Howard Stein (June 25, 1911 – February 2, 1980) was an American biochemist who collaborated in the determination of the ribonuclease sequence, as well as how its structure relates to catalytic activity, earning a Nobel Prize in Chemistry in 1972 for his work.

[4][6] Staunch advocates for the welfare of society, Stein's parents fostered his interests in the life sciences from a young age.

[4] Hans Thatcher Clarke, the chairman of the department at the time, was collecting many talented graduate students who would become the distinguished biochemists of the early twentieth century.

[4] William H. Stein and his wife traveled around the world and hosted many prominent scientists in their own home in New York City throughout his scientific career.

[8] Stein and Moore developed a method to quantify and separate amino acids with column chromatography, using potato starch as the stationary phase.

[3] They began testing other methods of separation, such as ion exchange chromatography, to reduce the analysis time, as it took two weeks to analyze one protein using the starch columns.

[8] Ion exchange chromatography reduced the time to 5 days during initial experiments, and eventually Stein and Moore whittled the process down even further with the help of Daryl Spackman, which resulted in the first automatic amino acid analyzer.

[10] With their success in improving the analysis time for amino acids, Stein and Moore began to determine the structure of an entire protein molecule, specifically bovine ribonuclease, in the early 1950s.