Object-oriented modeling is used in a growing number of commercial software development projects. But the plethora of approaches and corresponding CASE tools still prevents corporate users from migrating to object-oriented software development methods. Against this background the recent efforts of the Object Management Group (OMG) to standardize object-oriented modeling languages seem to promise substantial benefits: Not only will a standard allow to transfer a model from one CASE tool to another, it will also protect investment in training. However, at the same time it is questionable whether the state of the art in object-oriented modeling is mature enough to allow for standardization. In order to answer this question, we will briefly describe the proposals submitted to the OMG in January 1997. We will then show that there are still essential problems in designing modeling languages which have not been addressed yet.