I wouldn't think you'd need to make any changes. I've added a very ripe banana to breads before that didn't call for it just to use it up with no problems. It does make the bread moister!

Here is recipe for Peanut Butter Bread that I found somewhere on the net. I plan to make this soon.

Peanut Butter Banana Bread

2 1/2 cups all-purpose flour
1/2 cup granulated sugar
1/2 cup packed brown sugar
1 tablespoon baking powder
3/4 teaspoon salt
1/4 teaspoon ground cinnamon
2 large, ripe bananas, mashed (1 cup)
1 cup milk
3/4 cup chunky peanut butter
3 tablespoons vegetable oil
1 teaspoon vanilla extract
1 egg , slightly beaten
1 cup milk
Chocolate pieces
Peanut Butter Frosting

Preheat oven to 350 degrees F. Grease and flour two 8 x 4-inch loaf pans.

In a large mixing bowl stir together flour, sugars, baking powder, salt and cinnamon.

In another bowl combine mashed bananas, milk, peanut butter, oil, vanilla extract, and egg. Add to flour mixture, stirring just till combined. Stir in chocolate pieces. Pour batter into prepared pans. Bake for 50 to 55 minutes or until a wooden pick inserted near the center comes out clean.

Cool in pans for 10 minutes. Remove from pans; cool thoroughly on a wire rack. Wrap and store overnight before serving.

To serve, frost with Peanut Butter Frosting. If desired, top with crushed peanuts and miniature semisweet chocolate pieces. Slice to serve. Yields 24 slices (12 slices per cake)

Peanut Butter Frosting
3 tablespoons chunky peanut butter
2 tablespoons butter or margarine
1 cup sifted confectioners' sugar
1 teaspoon vanilla extract
1 tablespoon milk

In a small saucepan melt chunky peanut butter and butter or margarine. Remove from heat; stir in confectioners' sugar and vanilla extract. Stir in milk. Add more milk, if necessary, until of spreading consistency.

Makes about 1/2 cup.

Thanks, Nina, I saw that recipe, doing a search.
Recipe I posted is so easy looking, might try using the banana, as suggested in the first response.

Glenda, I agree that you probably don't have to change anything if you want to add one mashed banana. There is so little sugar already I don't think you would have to reduce it. Usually fruit purees replace some of the fat rather than liquid like milk, and since the only fat here is the peanut butter you don't want to reduce that at all right?

Do not try the recipe I posted, and it was a Paula Dean recipe.
It cooked in 40 minutes, which was way too long, and it was dry and the crust was knocking hard. Recipe said 50 minutes.

I felt like something was missing.

My GS liked it though, lol.
I didn't add the banana, but added 1/2 cup chocolate chips.

Should I complain to Paula :o)