[en] Using the particle identification system of the ARGUS detector at the DORIS II storage ring, operating at a centre of mass energy of around 10 GeV, a search has been made for particles with unexpected ionization produced in e⁺e^-. The production of antideutrons has been observed for the first time in e⁺e^- annihilation. No other unexpected ionizing particles were found in 84.5 pb^-1 of collected data. Upper limits are established for the production cross section of fractionally charged particles with masses up to 4 GeV/c², improving on previously obtained limits. Also the observation and analysis of D, F and Fsup(*) mesons relied to a large extent on the particle identification system. (author)