Parsec--scale radio jets in gamma--ray loud sources

We will present a multiepoch study of the three blazars 0954+658 (BL--Lac), PKS1510--089 (HPQ) and 1749+096 (BL--Lac). The first two sources are known to be $\gamma$--ray loud. Our study is based on milliarcsecond resolution polarimetric observations carried out with the VLBA at 8.4 GHz. The observations took place between January 1999 and May 2001. Superluminal motion is detected along the jet of PKS1510--089 and 1749+096, with $\beta_{app} \sim 10$ for all features. Magnetic field structure is revealed along the jets of 0954+658 and PKS 1510--089. The polarisation properties of the parsec--scale jets remain stationary in all sources, regardless of their total flux density variability in the radio band and of the presence of superluminal features.