This chapter addresses the following issues related to bias in hypnosis research: how it is known that hypnosis exists; how behaviors induced by hypnosis (rather than by other causes) may be isolated; and what precautions will insure that behaviors labelled hypnotic are really so. The difficulty of eliciting behaviors that are clearly a function of hypnosis are discussed, since people's motivations and behavior are similar both while awake and during hypnosis. Other factors include the role and possible bias of the hypnotist, as well as the attitudes, expectations, and characteristics of subjects who volunteer for hypnosis experiments. This report reviews recent research, focusing primarily on experimental rather than clinical data. It is concluded that although researchers may not be able to completely control for experiment-elicited bias, procedures may be used to indicate whether or not additional controls are necessary in future research. Further work is recommended to find cost effective controls for experimenter bias. It is also concluded that current, well-controlled research does not support the existence of unique, isolated behaviors caused by hypnosis; rather, these behaviors are strikingly similar to other kinds of experimental behavior.