Can I raise a dissenting voice? Do you REALLY want to expend the effort to distinguishing between NA and NaN in every single procedure and (presumably) every function, etc? It would be even worse if you added +/-Inf. My reaction is that there are better ways to spend time in developing the program. Anyone learning statistics or econometrics rapidly comes across the need to deal with missing values of several different kinds. Recognising that lx=log(x) for x <=0 causes a problem is a very elementary and early lesson. Masking it by, for example, setting lx=-Inf is likely to mislead. Since this would be very different from what most other programs do, it is likely to generate more problems of consistency across analyses performed using different packages. As far as I understand, the original argument was generated by the question: should 0*NA be 0 or NA? My personal view is that it should always be NA because it is always possible for the user to override this result by explicitly recognising that NA is really NaN and using conditional generate statements. The default of generating a missing value when there is any doubt is easily addressed by the user if a different result is required, but it is much safer for the unwary. Gordon Hughes