This paper outlines some of the basic ideas of the orienting response (OR) that have developed from the classical writings of E.N. Sokolov, in particular the effects of stimulus novelty, intensity, and significance upon the OR, and predictions about these effects on a range of physiological measures traditionally associated with the OR. Such measures include the GSR, respiration, heart rate, vascular responses, EEG, and pupil diameter. Unfortunately, many of the predictions of classical OR theory do not hold up when such a fine-grain analysis is undertaken. Possible conceptualizations of the discrepancies between Sokolovian predictions and empirical data are considered-should we accept such discrepancies as merely reflecting the imperfect nature of many OR indices, or seek other regularizing principles? Preliminary Process Theory has been proposed as one alternative account of the existing data base, and similarities and differences between it and Sokolovian theory are explored. The need for further investigation of such problems, in the very foundations of OR theory, appears to be of fundamental importance to the future status of the OR. An appendix provides a discussion between Barry and Sokolov on some of these issues. © 1990 Springer.