Blood samples will be taken from all N.F.L. players in training camp this summer to help create a benchmark for testing them for human growth hormone, according to a memo sent to players on July 12.

The memo said the samples would be used as part of a population study run by doctors hired by the league and the players union solely to determine the standards of a test to be introduced in the future.

The league and the players agreed to implement testing for H.G.H. in 2011 as part of their collective bargaining agreement, but they have been unable to agree on the procedures for the testing.

The memo said several other issues must be resolved before testing could be begin, including discipline for players caught using H.G.H.