Psychological distress persisting for weeks or more promotes pro-inflammatory immune dysregulation, a risk factor for a range of chronic diseases. We have recently shown that mindfulness training reduces distress among university students. Here we present an exploratory trial to study immune dysregulation in a cohort of students who were exposed to progressively greater stress as the exam period approached, and to explore whether mindfulness training mitigated this dysregulation. Healthy University of Cambridge students were randomised to join an 8-week mindfulness course (N = 27), or to mental health support as usual (N = 27). Psychological distress, immune cell proportions, cytokines, cRp and serum cortisol were measured at baseline and during the exam period. increased distress was associated with statistically significant increases in the proportion of B cells, regardless of trial arm (*p = 0.027). There were no other associations between any of the measured parameters, distress or mindfulness. Our finding that the proportion of B cells increases with psychological distress supports the findings of other studies. However, we found no evidence that mindfulness training is able to buffer the effects of psychological distress on healthy participants' immune system. In order to detect these effects, should they exist, larger randomised trials will be required. The human mind, brain and immune systems have much in common. They are complex, self-organising economies that recognise self from non-self, interact with the environment and possess ability to store information. The immune system alone is a highly distributed network of effectors, regulators and signals, which depend on dynamic balances to determine the best configuration for each environmental challenge. Prolonged systemic inflammation leads to increased risk of chronic diseases such as cancer, cardiovascular disease, diabetes, dementia and depression 1 , the most important global causes of morbidity and mortality. Thus, interventions that restore or maintain normal immune function in healthy and at risk populations are useful in preventing a range of mental and physical disorders 2,3. Even small improvements at a population level could lead to large reductions in morbidity and mortality 4. The immune, endocrine and nervous systems are known to interact with one another to provide a coordinated response to external stimuli, whether it be a physical insult such as wounding or an emotional stressor such as perceived stress (reviewed in Glaser et al.) 5. Acute stress promotes a pro-inflammatory state along with the "fight