An algebraic model for human interaction via information transmission is presented and discussed. Information transmission is schematized as the exchange of logical propositions among human subjects. As a first approach two interacting subjects are considered as being probabilistic automata described in terms of Boolean functions: in particular, a l6-tuple of probabilities defines the ‘mechanism’ of a subject. The description of an experiment (carried out on more than 300 subjects in order to justify such a drastical hypothesis) follows. Starting from a peculiar definition of the law of composition of the mechanism, an ad hoc quasi-Boolean algebraic structure is introduced. (It would be possible to force it to be a Boolean algebra but this disagrees with reality). In such a way it is possible to investigate more complex structures such as groups or many-person systems. Human subjects can be clustered into classes of ‘dominant’mechanism which are correlated with the results of classic psychological test (Minnesota). Further, the model gives a possible interpretation of usual psychotherapeutic practices such as the ‘silence’ and the ‘use of paradoxes’