The aim of this study was to evaluate the effects of two periods of intermittent exposure to hypoxia (428 torr) in rats over 12 months. The conditions of CIH4x4 (4 days in hypoxia, 4 days in normoxia, n = 50) and CIH2x2 (2 days in hypoxia, 2 days in normoxia, n = 50) were selected for simulating in this animal model the chronic-intermittent exposure to high altitudes experienced by Andean miners. We assessed mortality, weight, hematological parameters, and time course of resting heart rate and systolic blood pressure. In general, mortality increased during the first month, with a tendency to stabilize during exposure; it was associated with lower weights and with higher hematocrit levels, making these possible predictor factors. Intermittence produced an increase in hematocrit and hemoglobin concentrations as previously seen in most hypoxic models, compared with normoxia (NX, n = 30), but attained lower levels compared with chronic hypoxia (CH, n = 28). CIH4x4 and CIH2x2 had similar sustained elevations of systolic blood pressure (171 +/- 3 and 174 +/- 2 mmHg, respectively) versus the basal level (163 +/- 3; 163 +/- 3 mmHg), whereas CH did not. Heart rate suffered an equally sustained decrease in all exposed groups (343 +/- 14 beats/min). Exposure to chronic-intermittent hypoxia led to a mild polycythemia and to a decrease in heart rate. The effects of hypoxia were already evident during the first month of exposure and attained a more pronounced expression and stabilization during the third month.