Blood testing will not be introduced in time for next year's 20th anniversary London Marathon.
Reports had suggested that blood tests, which are more accurate than existing anti-doping measures, would be mandatory for entrants in the April race.
However, organisers yesterday confirmed there were no plans to introduce blood testing until the International Amateur Athletic Federation (IAAF) had ratified such procedures.
"The London Marathon supports moves by the Association of International Marathons for the introduction of blood-testing," said race director David Bedford.
"However, we cannot suddenly do this unilaterally. To my knowledge there is no test in place that we could possibly use for next year's race.
"Once a test is in place, which has been ratified by the IAAF and adopted by other big city marathons, then it will be in place in London."
Blood testing will detect erythropoietin (EPO), a drug used to boost the count of oxygen-carrying red blood cells which can dramatically improve stamina.
Meanwhile, world record holder Khalid Khannouchi has promised to set an electric pace at next year's Marathon.
The Moroccan smashed Brazilian Ronaldo da Costa's world best in Chicago last month, becoming the first runner to ever dip below two hours and six minutes. He arrived in London this week for a whistle-stop visit to check out the course in preparation for next April's race.
