[YEA] I have successfully used castor oil to treat toenail fungus. My baby toenail was completely taken over by fungus. It had a black line running through it as well (another sign of fungus). I did this treatment twice per day until the nail grew out: First, I put two drops of vinegar on the nail. Then I placed a bit of cotton soaked in castor oil directly on the nail and kept it in place with a bandage. The nail is completely healthy. It's been almost two years since the treatment.