Functional analysis is used to identify potential reinforcers by generating hypotheses about possible functions of a behaviour. Current methods of functional analysis emphasise observations of events, especially consequences, that occur in the immediate environment of the behaviour. While these methods are well suited for assessing behaviour that is reinforced frequently, they are less appropriate for assessing behaviour that is reinforced only intermittently. A new method for conducting functional analysis is presented that is designed to assess intermittently reinforced behaviour. The new method is illustrated using data that were gathered from an extension of a standard problem-solving format. Data are interpreted using the principle of revealed preference that arose from behavioural economics. The revealed preference method is illustrated using information provided by a client with a dependent personality disorder.