In the 1960's, H. Zassenhaus made three conjectures about torsion units and finite subgroups of the units in integral group rings. The strongest one (ZC-3) states: If H is a finite subgroup of the unit group of augmentation 1 in the integral group ring ZG, then H is conjugate to a subgroup of G in QG. In this thesis, we prove that ZC-3 holds for groups of order p^2q, where p, q are distinct primes.