Aims: To investigate the role played by employees' perceptions of their supervisors' interactional styles as a possible source of workplace stress that may be associated with increased morbidity and mortality rates from cardiovascular disorders in workers in the lower strata of organisational hierarchies. Methods: A controlled, quasi-experimental, field study of female healthcare assistants. Allocation to the experimental and control groups was based on participants' responses to a supervisor interactional style questionnaire. Experimental participants (n = 13) reported working under two divergently perceived supervisors at the same workplace, on different days. The control group (n = 15) worked either under one supervisor, or two similarly perceived supervisors. Ambulatory blood pressure was recorded every 30 minutes, over a 12 hour period for three days. Results: The control group showed a 3 mm Hg difference in systolic blood pressure (SBP) and a non-significant difference in diastolic blood pressure (DBP; mean difference 1 mm Hg) between the two supervisor conditions. The experimental group showed significantly higher SBP (15 mm Hg) and DBP (7 mm Hg) when working under a less favoured compared to a favoured supervisor. The degree of divergence in perceptions of supervisors shows a significant positive relation with the difference in blood pressure between the two workdays. Divergence in perceptions of interpersonal fairness is the strongest predictor of difference in blood pressure. Conclusion: An unfavourably perceived supervisor is a potent workplace stressor, which might have a clinically significant impact on supervisees' cardiovascular functioning.