Two hundred specimens of the cyprinid fishPuntius binotatuswere collected over a period of 1 year, February 1976–January 1977, from an irrigation canal in Palau Pinang, Malaysia. Six species of parasites were recovered:Dactylogyrussp.,Rhabdochona penengensisFurtado, 1965;Proteocephalussp.,Bothriocephalus acheilognathiYamaguti, 1934,Pallisentis gaboesMacCallum, 1918 andLamproglena minulaCapart, 1943. The prevalence and mean density of two ectoparasites (Dactylogyrussp. andL. minuta) and an endoparasite(B. acheilognathi)were examined in relation to season and host size. Fish were found to be free of these parasites in many months of the year. Prevalence and mean density ofDactylogyrussp. andL. minutawere found to be highest during the early part of wet season, whereas those ofB. acheilognathiwere found to be highest in the later part of wet season. Prevalence ofL. minutaincreased with increasing size offish, but mean density was least in the largest fish. Both prevalence and mean density ofB. acheilognathiwere highest in smaller fish, whereas that ofDactylogyrus sp.showed little variation in the three size–gro