Cores measuring 94 mm and 144 mm in diameter and having length-to-diameter ratios of 2-0, 1.0 and 0.75 were removed from beam specimens produced from different concrete mixtures. Standard cubes and cylinders were also produced from the same mixtures. Compressive strength tests were conducted on 216 standard and 530 core specimens. The test results obtained from core specimens were compared with those of standard specimens. The efftets of maximum aggregate size in concrete mixture, core diameter and type and size of the standard specimens on the interpretation of the core test results were examined. The test results showed that the maximum size of the aggregate affects the strength of the cores even when the diameter of the core is larger than three times the maximum size of the aggregates. The age of the concrete was found to be an important factor in the interpretation of the core strength results. Although the cores with a length-to-diameter ratio of 0.75 gave higher strength values, they may be used for the evaluation of the core strength results.