In this study, Argulus foliaceus L. (Crustacea: Branchiura) infection of one cyprinid fish species, rudd (Scardinius erythrophthalmus) in Lake Manyas, Turkey was examined on the basis of samples taken from on-site surveys carried out between December 1996 and November 1998. Of the 135 S. erythrophthalmus examined, 32 (23.7%) was infected with A. foliaceus. The distribution on microhabitat locality of A. foliaceus was found to be as follows: 3%, 3.2 +/- 0.5 specimens/fish on oral cavity; 6%, 4.9 +/- 0.5 on the gills; 6%, 5.9 +/- 0.9 on the fins and 6%, 8.9 +/- 1.5 on the skin. However, it was not a statistically meaningful differences among the microhabitat locality (P > 0.05). Moreover in this study, A. foliaceus infection was investigated depending on the years, and seasons, and host fish size.