Stress granules (SGs) and P-bodies (PBs) are related RNA- and protein-containing foci that store and silence mRNA in the cytoplasm – SGs are induced in response to stress, whereas PBs are constitutively present (but are further induced under stress). Both structures are known to be highly dynamic – but how are RNA and protein components shuttled in and out of the foci? To address this question, Graciela Boccaccio and colleagues (p. 3973) analyse the role of the motors dynein and kinesin in SG and PB dynamics. Using an RNAi approach in cell culture, the authors first show that dynein heavy chain 1 (DHC1) and the dynein adaptor BicD are both required for stress-induced SG formation and PB growth. By contrast, knocking down the kinesin-1 heavy chain KIF5B and kinesin light chain 1 delays the dissolution of SGs. Moreover, simultaneous knockdown of dynein and kinesin reverts the effects of single knockdowns (both on SGs and PBs), indicating that the balance between kinesin- and dynein-driven transport regulates SG and PB growth. Notably, the authors find no evidence that perturbing SG formation and dissolution affects global translational silencing. The finding that dynein and kinesin motors regulate SG and PB assembly in a push-pull manner provides new insight into the dynamics of cytoplasmic granules.