In a bowl, add the desired amount of ketchup for the number of persons to serve and according to quantity of seafood being served. Usually it will be about 1/2 - 1 cup of ketchup.

Add one to two tsp of horse radish, and then taste. Add more if needed.

Add lemon juice to give it that desired tang. Usually start with about 1/2 a teaspoon, and add more to taste.

If you get it to strong, simply add a little more ketchup.

Experiment to meet your taste buds likes and dislikes. Only you can be the real judge. Remember, a great cocktail sauce is not the main attraction, rather it compliments the seafood.