The locomotory behavior of Caenorhabditis elegans consists of four simple events, forward and backward movements, omega-shaped turns and rests. The wide variety of behaviors of this worm is achieved through a combination of these simple locomotions. To gain insight into the neuronal mechanisms regulating this locomotion, we analyzed the locomotory behavior of C. elegans over a long time period. In this study, we revealed the existence of at least two distinct behavioral states–pivoting and traveling–in the forward locomotion of C. elegans in the absence of food. Pivoting is characterized by pronounced directional switching and resulting in short-duration forward movement, whereas in the traveling state, forward movement is of longer duration. Pivoting has occurred when we transferred a well-fed worm to unseeded plate, and then transition to traveling has taken place, successively. We examined the function of chemosensory neurons in this behavioral alteration by laser-ablation. Duration of forward movement was shortened by the loss of any one of the six chemosensory neurons (AWA, ASE, ADF, ASH, ASI, and ADL). On the other hand, loss of AWC, ASK or AFD chemosensory neurons lead extension of duration of forward movement. Similar to the case for chemosensory neurons, ablation of AIA, AIY and AIB, AIZ interneuron resulted in short- and long- duration forward movement, respectively. These results suggested that C. elegans regulate their locomotion using multiple chemosensory and interneurons having opposed functions. [Jpn J Physiol 55 Suppl:S172 (2005)]