Patients are having to wait longer for treatment in accident and emergency units across Wales, according to the latest figures.
The Pontypridd and Rhondda NHS Trust was the best performing area
Only two out of 12 trusts reached the target of treating patients within four hours.
In September 2007, 89.7% of patients were seen within that time - slightly down on last year. The target is 95%.
The figures also showed that some patients were not being seen within eight hours.
The results varied from region to region across the country.
Cardiff and Vale NHS Trust was the worst performing area ,with 76.6% of patients seen within four hours.
The best performing were Pontypridd and Rhondda NHS Trust (95.9%) and North West Wales (95.3%).
The target that no patient should ever wait more than eight hours to be seen in a major A&E was also not being met, the statistics revealed.
The average around Wales for September 2007 was 98.4% of patients being seen within eight hours.
Jonathon Davies, deputy chief executive of Cardiff and Vale NHS Trust, acknowledged that many patients were waiting longer than they should for emergency treatment.
He said there was an increasing demand for emergency care, which meant more patients were experiencing delays, which the trust was "very concerned" about.
Mr Davies apologised to patients that had been affected, and said the trust was working with its public sector partners to identify alternatives to hospital admissions to alleviate the pressure.
Conservative Jonathan Morgan said waiting times could be cut by easing bed blocking and increasing A&E capacity.
"The assembly government needs to review the four-hour target to see how effective it is," he said.
"The fundamental problem is two-fold. One, we have not seen an increase in the capacity of A&E departments to deal with increased demands placed upon them by patients.
"And two, nothing has been done to alleviate the problem of bed-blocking."
He called on Health Minister Edwina Hart to ensure that local authorities fulfilled their obligation to help transfer patients out of hospital and into community care by introducing fines for those which failed to achieve it.
A spokesman for the assembly government said the health minister was determined to ensure that those trusts which did not reach the target during September raised their game.
"She has asked senior officials to focus specific attention on these trusts so that they improve performance," he said.
"The minister also met with trusts in south east Wales and the Wales Ambulance Service Trust this week to discuss emergency pressures, and has asked the trusts to work together and with other partners to address these issues."
The spokesman said almost 90% of patients were seen within the four-hour target.