using(SPWeb oWebsite = SPContext.Current.Site.AllWebs["Subsite_Name"])
{
SPRoleDefinitionCollection collRoleDefinitions = oWebsite.RoleDefinitions;
SPRoleAssignmentCollection collRoleAssignments = oWebsite.RoleAssignments;
SPRoleAssignment oRoleAssignment = new
SPRoleAssignment("DOMAIN\\User_Alias","User_Alias@Somewhere.com","Displ
ay_Name","Notes");
SPRoleDefinitionBindingCollection collRoleDefinitionBindings = oRoleAssignment.RoleDefinitionBindings;
collRoleDefinitionBindings.Add(collRoleDefinitions["Role_Definition_Name"]);
collRoleAssignments.Add(oRoleAssignment);
}