Germany's military could have as many as 275 suspected right-wing extremists in its ranks, with one soldier heard saying "Heil Hitler".
The armed forces counter-intelligence agency is looking into the claims after 143 cases were reported last year and 53 so far in 2017.
Among the incidents were soldiers performing Nazi salutes or making racist remarks against colleagues with migrant backgrounds.
It is illegal in Germany to show Nazi symbols, such as swastikas, in public or make salutes associated with Adolf Hitler's regime.
The country's defense ministry detailed the investigation in a letter to parliament and said some of the most serious cases had not been dealt with strongly enough.
In one case, a soldier was heard saying "Heil Hitler," "Heil our leader" and "Sieg heil, comrades".
The incident was passed to the military prosecutor and the public prosecutor's office but the soldier did not get an early dismissal or a service ban, said the defense ministry.