Upland cotton normally has four- or five-lock bolls with, occasionally, three- or six-locks being observed. A mutant type which consistently has six- to 10-lock bolls (averaging between seven and eight) was obtained from the Regional Cotton Germplasm Collection at Stoneville, MS (S.A. 0981 "Multiple Lock, West Tex"). In the genetic study of this trait, two multilock lines selected from S.A. 0981 were crossed with TM-1 and 'Westburn M', respectively. The parental, F₁, backcross and F₂ populations were examined. Multilock boll appears to be governed by a single, largely recessive gene.