In this paper, we discuss security aspects of interactive bilateral multi-attribute negotiations. We introduce this type of electronic negotiations and maintain that it will be an important functional aspect of business-to-business electronic marketplaces. We discuss the general application architecture and the process flow for this type of negotiations. We introduce the relevant security issues and show how these issues can be dealt with, especially within a business relationship where a lower degree of trust prevails. To this purpose, we introduce and discuss a protocol for secure interactive electronic negotiations.