This paper deals with two problems associated with input-output models: disaggregation and updating. National input-output models are commonly designed as general purpose models. Analysts with specialized interests will at times find that the segment of the economy on which their particular interests are focused is too highly aggregated. In this context, the procedure used for disaggregating the 7 mining sectors in the 1967 U.S. input-output table to 47 sectors is discussed. A second potential problem associated with input-output models arises from changes over time in the relationships between economic sectors. If the technical coefficients of the input-output model are not accordingly adjusted to reflect these changes, significant errors in the model's output may result. The two most prominent techniques designed to update the input-ouput model's technical coefficients, the ras and linear programing (lp) methods, are compared with regard to changes in U.S. national coefficients between 1963 and 1967.