Thousands of junior doctors across England are taking to picket lines as the row with the Government over a new contract escalates.
1. Why is this strike worse?
NHS leaders are more worried about the latest strike because junior doctors are withdrawing full labour, including emergency care. This puts the NHS under increased pressure, although routine operations and appointments have been cancelled so staff can concentrate on patients in most need.
2. What is the dispute about?
The Government is intent on introducing a new contract for doctors working up to consultant level to replace one it says is outdated.
Health Secretary Jeremy Hunt wants to cut the number of hours over a weekend for which junior doctors can claim extra pay, while offsetting this with a hike in basic pay.
This has proved a major sticking point in the row with the British Medical Association (BMA) - whether Saturdays should attract extra "unsocial" payments.
Currently, 7pm to 7am Monday to Friday and the whole of Saturday and Sunday attract a premium rate of pay for junior doctors.
The imposed contract, due to come into force in August, has an increase in basic salary of 13.5% but 7am to 5pm on Saturdays will be regarded as a normal working day. There will still be premium rates for Saturday evenings and all of Sunday.
The BMA has rejected these plans.
3. Wasn't there something about death rates?
Yes. Jeremy Hunt angered junior doctors by repeated references to higher death rates for patients in NHS hospitals at weekends.
While the research does suggest thousands more people may die following admission at weekends than during the week, researchers have been very cautious about suggesting that staffing issues are to blame.
Doctors accuse Hunt of conflating the arguments by saying that unless contracts are reformed immediately, patients will continue to die.
4. What happens now?
The BMA is launching a judicial review and other pressure groups have also launched legal challenges over the legitimacy of the contract.
There is a suggestion that doctors could walk out indefinitely if the Government imposes the contract.
5. What impact has the strike had on patients?
The latest strike will see more than 125,000 operations and appointments cancelled and needing to be rearranged.
This is on top of almost 25,000 procedures cancelled as a result of previous strike action.