Flaxseed (Linum usitatissimum seed) is widely used in food and natural health products. In our search for osteoclastdifferentiationinhibitors, some cyclic peptides isolated from flaxseed, known as the cyclolinopeptides, were discovered to have osteoclastdifferentiation inhibition activity. The osteoclastdifferentiation inhibition activity of cyclolinopeptides A–I (1–9) and their related derivatives