Objective: To conduct a phase 1 safety and tolerability trial of an oral rotavirus vaccine candidate RV3 in healthy volunteers. Methodology: Double blind placebo controlled trial of a single 1 mt oral dose (6.5 x 10(5) fluorescing focus units [FFU]/mL) in 10 healthy young men, 10 3-4 year old children and 10 3 month old infants with a 4 week surveillance period. The study was undertaken at a children's hospital and nearby community in Melbourne, Australia. Results: All subjects successfully completed the trial. There were no significant side-effects attributable to the vaccine preparation in any age group, No shedding of vaccine virus was detected by enzyme immunoassay. There was evidence of an immune response in serum and/or gut secretions in two of five vaccinees in each age group. Conclusion: RV3 rotavirus vaccine appears to be safe and well tolerated. Evidence of immunogenicity in some subjects after a single dose encourages further trials to determine immunogenicity after three doses, after reduction of viral dose, and without prior administration of buffer.