The large GTPase dynamin 2 (Dyn2) helps cells internalize material by clathrin-and caveolae-mediated endocytosis. Its role in other internalization mechanisms is controversial, however. Now, Mark McNiven and colleagues report that Dyn2 drives fluid-phase micropinocytosis (internalization of small amounts of extracellular fluid), one of several mechanisms that cells use to sample their external environment (see p. 4167). Inhibition of all four Dyn2 splice variants by anti-dynamin antibodies or RNAi, the authors report, reduces the uptake of the fluid markers dextran and horseradish peroxidase in serum-starved epithelial cells. Dyn2 inhibition has no effect, however, on the uptake of these markers in serum-or EGF-stimulated cells, which suggests that Dyn2 is required for fluid-phase micropinocytosis but not for stimulated fluid uptake via macropinocytosis. The authors also report that cells expressing dominant-negative mutants of two specific Dyn2 variants–Dyn2(ba) and Dyn2(bb)–endocytose less dextran than cells expressing wild-type Dyn2. This suggests that different Dyn2 splice variants have different endocytic functions.