rhesus monkey: see macaque.

Sand-coloured macaque (Macaca mulatta), widespread in South and Southeast Asian forests. Rhesus monkeys are 17–25 in. (43–64 cm) long, excluding the furry 8–12-in. (20–30-cm) tail, and weigh 10–24 lb (4.5–11 kg). They eat fruits, seeds, roots, herbs, and insects. They are held sacred in some parts of India. Hardy in captivity, highly intelligent, and lively, they make good pets when young but may become bad-tempered as adults. They have been used frequently in medical research. The determination of the Rh (from rhesus) factor in human blood involves reaction with the blood of this species. Seealso Rh blood-group system.

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Rhesus can refer to any of the following:

• Rhesus of Thrace, a king in Greek mythology
• S. Vivianus Rhesus, a Roman governor of Thrace
• In Greek mythology, a river-god, son of Oceanus and Tethys
• Rhesus (play), the Ancient Greek play once thought to be by Euripides
• Rhesus factor, associated with a blood type
• Rhesus Macaque, also known as the Rhesus Monkey