An experimental system for declaring and inferring type in Smalltalk is described. (In the current Smalltalk language, the programmer supplies no type declarations.) The system provides the benefits of type declaration in regard to compile-time checking and documentation, while still retaining Smalltalk's flexibility. A type hierarchy, which is integrated with the existing Smalltalk class hierarchy, allows one type to inherit the traits of another type. A type may also have parameters, which are in turn other types.