Free swimming cells of the ciliated protozoan Tetrahymena are attracted to certain chemicals by chemokinesis. However, a special type of chemotaxis in response to a chemical gradient is found in cells gliding very slowly in semisolid media. In contrast to classical chemotaxis by leukocytes, which is solely positive towards chemo-attractants, the oriented chemokinesis by gliding Tetrahymena involves both positive and negative elements. The major chemo-attractants are peptides and/or proteins, and they may be compounds which signal the presence of food in the natural environment of this freshwater phagotroph.