Investigations were made on whether or not freshwater fishes in the Sagami River were contaminated by the herbicides CNP (chloronitrofen), chlomethoxynil, molinate and benthiocarb (thiobencarb). Application of these herbicides to paddy fields is restricted during the rice planting season, so this investigation was carried out in July and the contamination levels of other months were compared. CNP was detected in all four species of fishes (pale chub, pike gudgeon, carp and crucian carp), and benthiocarb was detected in two species in July, 1980. The residual levels of CNP were from 0.055ppm to 0.61ppm, and those of benthiocarb were 0.02ppm and 0.10ppm. These values were similar to those found in pale chub, ayu, crucian carp and large mouth bass in July, 1981 tests; the residual levels of CNP were from 0.046ppm to 0.88ppm and those of benthiocarb from 0.04ppm to 0.11ppm, respectively. But in September, 1981, the residual levels were below a detectable level or detected only in very low concentrations. The bioconcentration ratio (concentration level in fish/concentration level in water) of CNP was supposed to be 420-8, 000 and that of benthiocarb 20-100, when estimated from the results of this investigation. But it was thought that the residual period in fish did not continued too long. Chlomethoxynil and molinate were not detected in any fish examined.