Arterial blood gas (ABG) sampling represents the gold standard for determining the patients' acid-base and ventilatory status. However, it has many drawbacks. This study assessed the relationship and agreement between arterial and capillary measurements in adult intensive care unit (ICU) patients. ABG and capillary blood gas (CBG) samples were obtained from 49 adult and 51 elderly (a total of 100) patients with cardiopulmonary disorder, cerebrovascular accident, intoxication, multiple trauma, and metabolic coma. All samples, collected at the same time, were analyzed. The kendall's tau rank correlation, unpaired t-test, paired-t test and Bland-Altman method which is used for measurement of agreement, were used for analysis. The median age was 65 years (min: 18, max: 90). There was a significant correlation between ABG