There are several SAS procedures that enable you to do maximum likelihood estimation of parameters in an arbitrary model with a likelihood function that you define: PROC MODEL, PROC NLP, PROC OPTMODEL and PROC IML.

The MODEL procedure in SAS/ETS software enables you to minimize general log-likelihood functions for the error term of a model.

The NLP and OPTMODEL procedures in SAS/OR software are general nonlinear programming procedures that can maximize a general function subject to linear equality or inequality constraints. You can use PROC NLP or OPTMODEL to maximize a user-defined nonlinear likelihood function.

You can use the IML procedure in SAS/IML software for maximum likelihood problems. The optimization routines used by PROC NLP are available through IML subroutines. You can write the likelihood function in the SAS/IML matrix language and call the constrained and unconstrained nonlinear programming subroutines to maximize the likelihood function with respect to the parameter vector.