Abstract Advances in the last few decades demonstrate the relevance of Pavlov's classification of behavioural types with respect to human individual differences and suggest that the hypothetical excitatory and inhibitory processes which he associated with these differences correspond to cortical and thalamic neuron populations of the diffuse thalamocortical system (DTS). Since the transmission properties or time constants of these DTS elements would correspond to the Pavlovian property of ‘strength’, and since they can be evaluated in human subjects (Robinson, 1981), it is possible to formulate hypotheses based on the fundamental principles of strength and balance which Pavlov employed to provide a causal explanation for temperamental types. A major finding is that covariation of the time constants equated with strength correlates 0.95 with covariation of extraversion and stability scores on the Eysenck Personality Questionnaire (EPQ). This result provides unequivocal support for the relationship between human individual differences and properties of the nervous system postulated by Pavlov and it also confirms the neurophysiological underpinning of Eysenck's influential theory of human personality. In addition, the relationship between Pavlovian and Eysenckian concepts is clarified and EEG parameters are meaningfully related to personality differences.