Observations of biological choruses in the ambient noise of tropical waters of the east Indian Ocean, the west Pacific Ocean, and the Timor Sea near Australia are described. These choruses occurred for a few hours at a time and had most energy at frequencies between 400 Hz and 4 kHz, with spectral peaks mainly at 800 Hz, 1.6–2 kHz, and 3 kHz. During choruses, noise spectrum levels rose up to 30 dB above the usual background noise. Statistics of occurrence of the evening choruses indicate that they would occur on most, if not all evenings at the locations of measurement and are probably fairly widespread in and near shallow waters of the region. As well as these regular evening choruses, there were also transitory choruses which were observed at various times of day over periods of a few days but not before or after. Possible sources of the choruses are discussed. There are at least three sources of the regular evening choruses, possibly fish or sea urchins. Some of the transitory choruses, spectrally similar to the regular choruses, were composed of intense clicking sounds, apparently from sperm whales.