We have analyzed amplification without inversion (AWI) in the presence of c
ollisions in V and Lambda three-level systems. We have found that collision
s cause a very important contribution to the quantum interference that redu
ces absorption in the case of the V system. In the Lambda system the effect
of collisionally induced quantum interference on AWI is smaller than in th
e V system but the Lambda system offers new interesting possibilities of in
coherent pumping on a low-energy transition. This possibility allows obtain
ing frequency up-conversion of the amplified radiation with respect to both
pumps, the coherent as well as the incoherent one.