Behavior analysts have conceptualized chaining from two different positions: Position 1 (responses function as discriminative stimuli for subsequent responses) and Position 2 (responses produce stimuli that function as discriminative stimuli for subsequent responses). Twenty-four mentally retarded adults learned a chain of circuit board assembly responses consisting of placing resistors in the board and pressing switches. Lights came on after switch responses. After learning the chain, each subject was exposed to three experimental conditions (counterbalanced): (a) altered stimulus location, (b) altered stimulus sequence, and (c) missing stimulus. Although a clear test of Position 1 was not made, some support for Position 2 was obtained. Alternate interpretations were discussed.