The ciliate Strobilidium sp. and 2 flagellates, Chrysochromulina simplex and Gymnodinium sp., were exposed to predator-generated feeding currents, and their escape responses were quantified using 2- and 3-dimensional video techniques. All 3 studied organisms responded by escaping at a defined distance to their predators. A critical threshold fluid deformation rate of escape of 3.6 s(-1) was estimated in a quantifiable siphon suction flow field for the ciliate Strobilidium sp. Using previous published models and the critical deformation rate estimated here, I predicted the reaction distance of Strobilidium sp. to the copepod Temora longicornis. The predicted reaction distance fit closely that measured, When the flagellates were exposed to the flow field of the ciliate Uronema filificum, they both responded up-stream to the feeding current. From the distance at which the flagellates responded to the ciliate, the critical deformation for escape for both the flagellates was estimated to range between 6.9 and 14.5 s(-1). The critical deformation rate of flagellates proved to be slightly higher than that of ciliates. I speculate that this reflects that ciliates are the main predator on flagellates while ciliates themselves have a higher deformation sensitivity in order to avoid copepods that overall have a more well-developed sensory apparatus.