<正> The mutagenicities of 22 kinds of foods

including soy sauce

fish sauce

shrimp paste

sausages

sundried fishes

rice cracker

deep fried pork skin

salted vegetable and spices after nitrite treatment

were detected by meansof Ames test with preincubation.Mutagenicity assay was employed on Sal-monella typhimurium TA100

and meanwhile

the validity of each experi-ment was checked by using the known mutagen

AF-2

as the positivecontrol.16 kinds of foods showed marked direct-acting mutagenicity towardSalmonella typhimurium TA100 after nitrite treatment.Shrimp paste prod-uced in Bankok was the strongest one among these samples.Its specificmutagenicity was 37000 revertants/g.The amount of precursor

tyramine

in shrimp paste was estimated fromthe area of tyramine peak on HPLC by using the authentic tyramine as thestandard.Results showed that one gram shrimp paste contained 439μgtyramine.The mutagenicities of foods suggested that nitrosatable precursors

suchas amine or amide

were present in foods

and they could be converted intoendogenous carcinogen

nitrosamine

in vivo.Therefore

detection of muta-genicities of foods has significance in preventing cancer.