Homemade. Cost is a small fraction of retail. However, unless you really know what you're doing, I don't recommend making it yourself. You need pure silver, a properly regulated electrolysis apparatus, and careful monitoring of electrolytic current. I used to get it at a local vitamin shop, but can't remember the brand. It was around $30.00 a bottle. Do not take larger quantities thinking more is better... One teaspoon twice a day (morning and evening) is all I take and probably all you'll need. You might want to check out a site with colloidalsilver in the name... their site seems quite legit.