The family of a nurse who went missing while taking part in a clinical trial for malaria said today his disappearance was "totally out of character".
Police said Matthew Lloyd needs immediate treatment to counter the drugs given to him during the trial.
The 35-year-old, who works at Southampton General Hospital, phoned in sick last week, Hampshire Police said.
Mr Lloyd, from Shirley, Southampton, then failed to attend an appointment in Oxford for the trial on Thursday and has not been seen since.
His parents, Doreen Holland, 64, and Michael Holland, 74, along with his sister Claire Holland, 31, made an appeal for help in finding him on ITV1 show Daybreak today.
Mrs Holland said: "We are completely lost. We have absolutely no idea. It's totally out of character for Matthew.
"Usually, once he he starts a project of any sort he will follow it through. He's not one to sort of just leave it halfway through.
"We just have no idea whatsoever what has become of him or where he is. None of his friends seem to know."
She said money had been taken out of his bank shortly before he disappeared.
"We thought it would be perhaps for bus money to get wherever he had to get the coach," she said.Reuse content