The purpose of this study was to measure serum adenosine deaminase (ADA) and ceruloplasmin (CP) activities in the second trimester pregnants who had high age and down syndrome (DS) risk as compared with non-pregnants. This preliminary study was made with 280 pregnants who gave blood samples for Down Syndrome risk screening program in our laboratory. The control group was formed with non-pregnants at the same age groups (35).The results of AFP (a-fetoprotein), hCG (human chorionic gonadotropin) and uE3 (unconjugated estriol) measured in the blood samples taken from the pregnants were evaluated as low or high risk with cut off 1/250 by using Prisca Prenatal Risk Calculation Program. Pregnants were grouped as high risk group (30), low risk group (170) and group with high risk according to age (80) in terms of Down Syndrome risk according to these results. Serum ADA and CP activities were measured in all groups and controls by spectrophotometric methods.Serum ADA activities were lower in pregnants with low DS risk (p<0.001), in all pregnants (p<0.01) and in pregnants with high age risk (p<0.01) and higher in pregnants with high DS risk (p<0.05) when compared to the control group.Serum CP activities were significantly higher in all pregnants, in pregnants with low DS risk, in pregnants with high age risk (p<0.001 in all groups) and in pregnants with high DS risk (p<0.05) when compared with the control group.Serum CP activities were low (p<0.001) and serum ADA activities were high (p<0.001) in pregnants with high DS risk according to pregnants with high age risk and pregnants with low DS risk. When pregnants with high DS risk were evaluated according to their age groups, low serum CP activities and high serum ADA activities were observed in 35-41 age group (p<0.05).As a result, we have found that serum ADA and CP activities were changed in pregnant women. These changes in serum CP and ADA activities due to pregnancy being different in groups with high DS risk and low DS risk indicate that the usage of these tests for screening test should be evaluated with further studies.