[A regression model in which the disturbances exhibit a certain type of heteroscedasticity is considered. Maximum likelihood methods of estimation are developed and compared with the two-step estimation procedure. A likelihood ratio test for heteroscedasticity is suggested.]

[This paper presents the theoretical development of bounds tests and exact tests for serial correlation in the context of a simultaneous equation model which are analogous to those developed for single equation models. The powers of the exact tests are estimated and compared using Monte Carlo simulation of a three equation model.]