The news could be potentially damaging to the receivers' stock during this weekend's NFL draft.
Harvin was considered a first-round pick after leaving the University of Florida following his junior season. Tate was considered a possible second- to fourth-round pick after a solid college career at North Carolina.
Joel Segal, the agent who represents both players, didn't return messages from FoxSports.com seeking comment.
NFL teams received the drug-test results earlier this week, according to FoxSports.com.
Sources told FoxSports.com Harvin and Tate were the only two high-profile players to flunk their combine drug tests, and one of the sources said that fewer than a dozen players tested positive for recreational drugs.
Players who failed the tests are subject to entry into the NFL's substance-abuse program.
Harvin finished his college career with 133 receptions for 1,929 yards and 13 touchdowns and 194 carries for 1,852 yards and 19 scores. He averaged 9.5 yards per carry and 11.6 yards every time he touched the ball. He also posted a strong 4.39 seconds in the 40-yard dash at the combine.
He was at his best in big games, earning MVP honors in the 2006 Southeastern Conference championship game and totaling 171 yards and a touchdown in a victory over Oklahoma in the Bowl Championship Series national title game in January.
He lined up at receiver, running back and quarterback for the Gators but expects to do even more at the next level because several teams have already talked to him about returning kickoffs and punts.
Tate finished his career with an NCAA-record 3,523 career combined kick-return yards. Before tearing two knee ligaments midway through his senior year, he averaged 23.5 yards on his 16 receptions.
Tate, still recovering from his injury, didn't work out at the combine.
Information from The Associated Press was used in this report.