In some aqueous plant extracts the formation of nanoparticles, microparticles and macroparticles has been observed. In the present investigation the particle formation in aqueous infusions of Harungana madagascariensis LAM. EX. POIR., a medicinal plant, was investigated using photon correlation spectroscopy (PCS) and scanning electron microscopy (SEM). The results show that nanoparticles with mean diameters of 220 nm are formed in aqueous infusions of the dried leaves of Harungana. The particles have an almost spherical shape. In aqueous infusions of the dried stem bark nanoparticles with a mean diameter of 242 nm (PCS) are observed at 25 degrees C. The particle size distribution has a maximum in the range of 200 nm to 300 nm. Nanoparticles can be detected in infusions of the leaves and the bark in the range of 25 degrees C to 55 C. The mean diameter of the nanoparticles in preparations of the bark is temperature dependent: At 55 degrees C the mean diameter is 144 nm, at 30 degrees C 197 nm and at 25 degrees C 242 nm. Lower temperatures result in higher count rates. In infusions of the leaves the mean diameters vary between 220 (25 degrees C) and 139 nm (55 degrees C). The particle formation was investigated at pH 2.2, 4.0 and 7.4 at 37 degrees C. Nanoparticles are detected in infusions of the leaves and the stem bark at each pH. The pH value has an influence on the mean diameter and the count rate.