The normal value of colloid-osmotic pressure (COP) was determined in male and female adults between 20 and 40 years old. Any differences of this value related to sex and age were investigated. It was found the statistical correlativeness of COP obtained with an oncometer and that calculated with Landis-Pappenheimer equation (F1) and the modified equation (F2) of the same authors. Two groups, each of 50 males and 50 females were formed. Those persons with altered routine laboratory tests that could modify COP were discarded. COP was determined with IL 186 Weil Oncometer and also calculated with both Landis-Pappenheimer equations (F1 and F2). An statistical analysis was made to see if age had any influence on COP. Results in males, measured COP was 27.22 +/- 2.51 torr, calculated COP by F1 was 26.646 +/- 2.38 torr, and calculated COP by F2 was 27.814 +/- 2.43 torr. In females, measured COP was 26.8 +/- 1.71 torr, calculated COP by F1 was 26.9476 +/- 2.005 torr, and calculated COP by F2 was 28.09 +/- 2.0984 torr. Measured COP regardless sex was 27.01 +/- 2.15. Using the variance analysis and the minimal significative differences (MSD) it was seen that measured COP and calculated COP by F1 can be used either one with 95 per cent of credibility in healthy ambulant adult. Using the aforementioned statistical procedure it was noted a lower figure between 30 and 35 years that at any other studied age.