Abstract: To assess the changes that occurs in serum constituents that kept in contact with the clot with time and under different storage temperature. The clotted specimens were allowed to stand at 4 or 30°C for 0, 3, 6 or 24 h and then assayed. Three rams were used in the study, blood samples were collected via jugular vein and divided into 7 plain tubes (totally, 21 blood samples used). Three tubes were centrifuged within 30 min of dispensing the aliquots, these sera represented initial (zero time) values. The remaining 18 aliquots were divided into two equal groups; one group was stored at 4°C in a refrigerator and another one at 30°C in an incubator. Serum kept in contact with the clot at 30°C showed significant decreases in serum albumin level and significant increases in serum globulin levels at 24 h. Serum kept in contact with the clot at 4°C showed significant increases in creatinine levels at 3 and 6 h and significant increase in serum phosphorus level at 24 h. In conclusion, serum samples for total protein, BUN and magnesium can be harvested after 24 h storage at room temperature or refrigerator. For creatinine serum must be harvested before 3 h storage at 4°C, for albumin and globulins serum must be separated before 24 h at room temperature.