This paper presents first experimental results for an Internet Protocol (IP) telephony-based steganographic method called lost audio packets steganography (LACK). This method utilises the fact that in typical multimedia communication protocols such as Real-time Transport Protocol, excessively delayed packets are not used for the reconstruction of transmitted data at the receiver; that is, these packets are considered useless and discarded. The results presented in this paper were obtained on the basis of a functional LACK prototype and show the method's impact on the quality of voice transmission. Achievable steganographic bandwidth for the different IP telephony codecs is also calculated. Copyright © 2012 John Wiley & Sons, Ltd.