Less money is being spent on the NHS per head of population in Wales than in the rest of the United Kingdom, according to official figures.
Labour says spending comparisons between nations are difficult
Conservatives called it evidence of Labour's failure to invest in health.
In response, the Welsh Assembly Government said it was difficult to draw direct spending comparisons with England, Scotland and Northern Ireland.
Health economist Professor Ceri Phillips said there were signs that health was improving in Wales.
The figures, in a Department of Health memorandum, showed total spending on the NHS in Wales had risen by 186% since devolution in 1999.
In England it rose by 224%, while in Scotland by 205%.
It means the amount spent per head of population in Wales is £1,420, which is up to £330 less than other parts of the UK.
Welsh Conservative health spokesman Jonathan Morgan AM said: "The health service in Wales is facing serious problems, from mounting deficits and long waiting lists, to the lack of NHS dentists and increased bureaucracy.
"These figures confirm that NHS Wales is set to fall even further behind the health service in other parts of the United Kingdom.
"Patients in Wales are paying the price for the glaring and growing differences in health expenditure between Wales and the other nations of the UK.
"Since Labour came to power they have delivered an NHS in Wales which is over-managed, over-administered, and under-resourced.
Wales is spending more on public health promotion
In response, the assembly government said drawing direct comparisons between the different home countries was fraught with difficulty.
A spokesman said: "Estimating direct comparison between the home countries is extremely difficult because of the differing pattern of health and care delivery in each of the UK administrations."
As examples, the assembly government said that much regulation and research and development spending was not devolved "while social care funding is often incorporated directly into the revenue support grant for local government".
"Equally it has always been recognised that there is a higher level of spend in the devolved administrations in Northern Ireland and Scotland.
Prof Phillips, of Swansea University, agreed that it was "very difficult" to make comparisons between spending on health in the different countries.
He said Tories were "probably trying to make something out of data which itself recognises it's dubious to make comparisons with."
He said Wales spent a lot more on health promotion and public health, which should reap benefits in the future while the emphasis in England had been on cutting waiting lists.