Although much is known about the acute and chronic effects of sustained hypoxia, less is known about the effects of intermittent hypoxia. The purpose of the present study was to elucidate the influence of intermittent hypoxia at rest on performance, cardio-respiratory and haematological adaptations in apnoea trained subjects. Nine apnoea trained (T) subjects (mean maximal static apnoea duration 252 s±72; mean maximal dynamic apnoea distance 68 m±25) and five healthy controls (C) were studied. No significant differences were found between the two experimental groups in anthropometric data, performance capacity, resting cardio-metabolic variables and lung volumes. Comparisons between T and C also showed that resting red blood cells, haemoglobin, hematocrit, neutrophils and procalcitonin were significantly lower in T group while platelets and linfocites were significantly higher in T group. However, in T group, significant differences were found in some physiological responses to graded cycle-ergometer exercise test (ventilatory equivalent: 38.63±7.77 vs 30.73±5.65, p< 0.05; heart rate max: 176±12 vs 158±15, p<0.02; respiratory exchange ratio: 1.16±0.05 vs 1.10 ± 0.02, p<0.03). Finally, in T group, static apnoea duration was positively correlated with Fat Free Mass (r²=0.3791). It is not possible to state, however, whether these changes in apnoea trained subjects reflect an adaptive response to a prolonged environmental stress.