Volunteers will be able to choose what they eat and drink during the trials
A US company is offering free holidays in Mexico and Guatemala for volunteers on a diarrhoea drug programme.
Vaccine manufacturer Intercell is offering up to $1,500 (£938) to cover flights and accommodation.
In return, the volunteers - being recruited in the UK and Germany - will wear vaccine patches, and give blood and faeces samples.
The trial is in a part of the world where travellers' diarrhoea is rife. A total of 1,800 volunteers are needed.
Intercell's clinical director, Nigel Thomas, told the UK's Independent newspaper: "We are looking for people who have already planned to go to Mexico or Guatemala and think this would add another interesting aspect.
"It is almost like going on a package holiday. They will be met by a concierge who will take them to their hotel and arrange for them to give their first blood sample within 48 hours."
According to the recruitment website, to be eligible for the programme, known as Trek Study, volunteers must be:
- between 18-64
- in general good health
- travelling to Mexico or Guatemala for at least seven days before May 2010
- willing to maintain a study diary for 17 days
Volunteers will be discounted if they have already received a cholera or diarrhoea vaccine, or if they have already developed diarrhoea travelling in a developing country in the past year.
Intercell's vaccine has already been tested on a smaller group of American volunteers.
According to results published in medical journal The Lancet last year, it reduced the incidence of diarrhoea by some 75%.