The present experiment investigated whether the gambling of American Indian (AI) and non-AI participants would be sensitive to the actions and/or ethnicity of another gambler (i.e., a confederate) when playing a slot-machine simulation. Eight male AIs and eight male non-AIs participated in five gambling sessions. In one, the participant gambled alone. In the other four, the participant played in the presence of a confederate of the same or different ethnicity who gambled the entire session or quit after playing five times. The gambling of the AI and non-AI participants did not differ, nor was either group sensitive to whether the confederate was AI or non-AI. Gambling behavior was altered by the confederate's actions, with participants gambling less when the confederate left the session than when alone or when the confederate stayed and gambled. These results suggest that the differences in gambling problems between AIs and non-AIs reported in the overall literature may not be a function of ethnicity per se. They also suggest that the actions of other gamblers may inhibit gambling, which may have treatment implications. (Contains 1 footnote and 1 figure.)