SharePoint Web Service UserGroup is used to work with users and groups of SharePoint website.
http://server/_vti_bin/UserGroup.asmx
Methods of SharePoint Web Service UserGroup* AddGroup
* AddGroupToRole
* AddRole
* AddRoleDef
* AddUserCollectionToGroup
* AddUserCollectionToRole
* AddUserToGroup
* AddUserToRole
* GetAllUserCollectionFromWeb
* GetGroupCollection
* GetGroupCollectionFromRole
* GetGroupCollectionFromSite
* GetGroupCollectionFromUser
* GetGroupCollectionFromWeb
* GetGroupInfo
* GetRoleCollection
* GetRoleCollectionFromGroup
* GetRoleCollectionFromUser
* GetRoleCollectionFromWeb
* GetRoleInfo
* GetRolesAndPermissionsForCurrentUser
* GetRolesAndPermissionsForSite
* GetUserCollection
* GetUserCollectionFromGroup
* GetUserCollectionFromRole
* GetUserCollectionFromSite
* GetUserCollectionFromWeb
* GetUserInfo
* GetUserLoginFromEmail
* RemoveGroup
* RemoveGroupFromRole
* RemoveRole
* RemoveUserCollectionFromGroup
* RemoveUserCollectionFromRole
* RemoveUserCollectionFromSite
* RemoveUserFromGroup
* RemoveUserFromRole
* RemoveUserFromSite
* RemoveUserFromWeb
* UpdateGroupInfo
* UpdateRoleDefInfo
* UpdateRoleInfo
* UpdateUserInfo