Listening to Mozart improves the outlook for mice undergoing heart transplants, a study has found.
Verdi had the same effect, increasing the time before the organs failed - but New Age music from Enya had no impact.
Scientists traced the response to the spleen, where changes occurred to levels of immune system signalling molecules and cells.
The Japanese researchers were unable to say whether music could influence organ rejection in humans.
But they pointed out that music was known to reduce stress, enhance relaxation, distract from pain and improve the results of clinical therapy.
For the study, laboratory mice were given heart transplants and exposed to one of three types of music - Verdi's opera La Traviata, a compilation of Mozart performances, and New Age music by Irish star Enya. A number of mice were made to listen to non-musical monotone sounds.
Exposure was for six days from the time of surgery.
Compared with Enya and monotone sounds, Verdi and Mozart significantly prolonged transplant organ survival, in some cases more than doubling it.
Immune system effects in the spleen were found to be the cause.
Listening to classical music was associated with lower levels of immune system signalling molecules interleukin-2 and interferon gamma. Levels of the anti-inflammatory molecules interleukin-4 and interleukin-10 were increased, together with numbers of immune response-regulating white blood cells.
The scientists, led by Dr Masanori Niimi, from Teikyo University in Tokyo, wrote in the Journal of Cardiothoracic Surgery: "Our findings indicate that exposure to opera music, such as La Traviata, could affect... aspects of the peripheral immune response... resulting in prolonged allograft (transplanted organ) survival."