Several theorists have hypothesized that physical child abusers experience physiological hyperreactivity to stressors, particularly stressful child interactions associated with child rearing. Experimental evidence generally supports the physiological hyperreactivity hypothesis, although there are some contradictory and inconsistent results within individual studies and across studies. Research also indicates the physiological hyperreactivity of physical child abusers and those at risk for being physically abusive occurs during a wide variety of stimulus situations, including aversive child-related stimuli, nonaversive child-related stimuli, and aversive non-child-related stimuli and during periods when no overt stimulus is present (resting or baseline periods). Recommendations concerning procedural and methodological improvements are offered to enable future researchers to better address unresolved issues related to the physiological hyperreactivity hypothesis. 50 references and 1 table