The first question on here was if it uses standard size tennis balls. The answer was YES. However, it does NOT. It comes with 3 mini balls and the are the only size that fits. Too small for my dogs.After contacting the seller they promptly offered a full refund. Great customer service. I've adjusted the rating to reflect the great customer service & the fact that there are 2 sizes and I can only assume that the larger one actually uses real Tennis Balls.Just keep in mind when ordering that there are 2 sizes of the throwing toys and the smaller ones uses and includes 3 balls that look and feel like tennis balls but aren't much larger than a Golf Ball. The balls that are included also tend to split in half when dogs chew on them.