1 c. soy sauce
1/2 c. brown sugar
1/2 c. vinegar
1/2 c. pineapple juice
2 tsp. salt
1/2 tsp. garlic powder
1/2 tsp. onion powder

Mix all ingredients and bring to a boil; cool. Marinate beef for a minimum of 4 hours (also excellent for shish-kebab).