Chinese swimmer Chen Xinyi was provisionally suspended Friday from the Rio Olympics after testing positive for a banned substance, while Bulgarian steeplechaser Silvia Danekova and Polish weightlifting champion Tomasz Zielinski were excluded.
The decisions were taken by the Court of Arbitration for Sport (CAS), which for the first time in Olympic history is holding hearings into doping cases.
Chen, who had been due to compete Friday but didn't start, has tested positive for hydrochlorothiazide and has "accepted a provisional suspension" while her case is fully processed, the court said.
Chen failed a doping test in Rio de Janeiro on August 7, the Chinese news agency Xinhua reported, citing the Chinese Swimming Association. The 18-year-old swimmer has asked for an examination of the B sample.
CAS said that a final decision on Chen would be issued "before the end of the Games." She had finished fourth in the 100-metre butterfly on Sunday.
The three athletes had the first failed doping tests at the Rio Olympics, which run through August 21.
Chen tested positive for a diuretic, Danekova for a stimulant of red blood cell production and Zielinski for a steroid.
The court expelled Danekova and Zielinski from the Olympics after all of their samples were processed.
Danekova, 33, had been tested on July 30 immediately upon her arrival in the Olympic Village. She had been due to compete in Saturday's 3,000m steeplechase heats.
She told Bulgarian broadcaster bTV she would now end her athletic career.
Bulgaria's Sports Ministry condemned Danekova, saying in a statement: "It is inadmissible that the image of Bulgaria is destroyed in this way and a stain placed on the entire Bulgarian sport."
Zielinski, 26, had undergone his out-of-competition test on July 31. The 94-kilo category lifter has a gold from the 2016 European championships and a silver from the same event in 2014.
Nearly 2,400 doping tests have been conducted in Rio since the opening of the athletes village on July 24, according to the International Olympic Committee, comprising 2,033 urine tests, 130 blood tests and 232 biological passport controls.
The IOC plans to carry out some 5,500 doping tests of the more than 11,000 athletes taking part in the Games.