This study investigates possible sources and directions of cross-linguistic influence on vowel reduction and speech rhythm produced by four trilingual speakers with different L1s in their L2 (German or English) and L3 (English or German). It was shown that, compared to native speakers, the speakers produced distinct differences in these phonological processes. The data do not give conclusive evidence for an L1 influence on these prosodic patterns in the speakers' L2 and L3. A positive effect of the L2 on the L3 is possible, but the results also show that the phonological properties of the L3 have an important influence on L3 productions. (Contains 4 tables and 4 figures.)