Two young clubbers suspected of taking ecstasy have died after separate dance music events at London's Alexandra Palace this weekend, police said.
The men, aged 20 and 21, were admitted to a north London hospital this morning and were pronounced dead within seven hours of each other.
The 21-year-old is thought to have attended an all-night party called Bass Culture, which started on Friday and continued into Saturday.
Billed as the biggest bass music all-nighter taking place in the country this year, it featured 30 drum and bass, dubstep, hip hop and electro acts playing across three giant stages.
The 20-year-old is believed to have attended a night called Epic, which ran into Sunday. Acts performing at the event included top DJs Eric Prydz, Pete Tong and John Digweed, and the band Death in Vegas.
A second 20-year-old man who was also believed to have attended the event last night was admitted to hospital as well and remains in a serious but stable condition today.
The Metropolitan Police said the cause of the deaths and injury was yet to be established but confirmed that one line of inquiry was that the men may have taken illegal substances, possibly MDMA - the chemical name for ecstasy.
They issued an urgent appeal for other clubbers to seek medical attention following the unexplained deaths. Detective Inspector Rita Tierney said: "Although it is too early to say what caused these men's health to deteriorate, we are investigating the possibility that illegal drugs may have been involved.
"If you have taken what you believed to be MDMA, or any other substance, during this weekend's events at Alexandra Palace, and are now feeling unwell, I would strongly urge you to attend your nearest hospital as soon as possible."
They appealed for anyone who had attended either of the events or had any information that could assist the investigation to call 0208 345 0737.