Patients are facing six-month waits for some diagnostic tests, statistics show.
It is the first time such figures have been published
It is the first time the so-called hidden waits have been published - to date hospital waits in England have measured diagnosis to treatment.
The government's approach to judging waits has been attacked in recent years for not giving a true picture.
Patients have been waiting for longer than six months for nearly an eighth of the 800,000 tests due to be carried out - with some waiting for more than one.
A similar number of waits were between 13 weeks and 26 weeks, with the rest - three quarters - being under 13 weeks.
The average wait at the end of April was seven weeks.
The figures, for 15 of the most common diagnostic tests including scans, internal examinations and hearing tests, mean that for many patients the wait for diagnosis is as long as the wait for treatment.
It has left many to predict the government faces a tough challenge meeting its targets.
By the end of 2008, no-one should have to wait longer than 18 weeks for the whole patient journey, which starts from the point of GP referral for tests and includes having those tests, getting diagnosed and starting treatment.
At the moment, almost everyone is treated in six months, but that is measured from diagnosis to treatment.
Ministers said by April next year diagnostic waits will be limited to 13 weeks.
Health Minister Andy Burnham said: "This transparency is unprecedented in the history of the NHS.
"This is the first time since the foundation of the health service that any government has taken action to identify and tackle waiting lists for diagnostic tests."
Since November 2005, patients waiting longer than 26 weeks for scans have been offered appointments at alternative hospitals and clinics.
In April this was reduced to 20 weeks.
But critics said the waits were too long.
Professor Janet Husband, president of the Royal College of Radiologists, said although progress was being made there were "still lengthy waits".
Steve Webb, health spokesman for the Liberal Democrats, who made hidden waits a feature of the last election campaign, said it was a "disgrace" the government had waited so long to publish the data.
"I am sceptical as to whether the 18-week target can be achieved."
Shadow health secretary Andrew Lansley said: "The government's record in tackling diagnostic waits is one of failure."
And Michael Summers, chairman of the Patients Association, said: "In too many parts of the country, patients are waiting too long for diagnosis.
"It is encouraging the government is publishing this data and we must now try to reduce waits."
And individual patients said if the government did speed up diagnosis, it would make a huge difference.
Brian Miller, who waited nine months for heart tests at Luton Hospital, said: "If the diagnosis process is speeded up it would give me peace of mind knowing what was wrong and then I would get treatment faster. The quicker that they do that the better for me."