One of the more unusual commissions Greek-French composer Iannis Xenakis ever received came from the International Society for Cardiovascular Surgery. For their 1981 World Congress in Athens, he was asked to compose a choral work using as text the Hippocratic Oath that all medical practitioners swear when setting out on their professional career. Prior to this, Xenakis had only composed two works for a cappella voices: Nuits (1967), and À Hélène (1977). The first piece is an intense, complex work full of extended techniques and wild sonorities; the second is a pared-down, two-part chant setting an ancient Greek text by Euripedes in the simplest possible fashion.
Serment falls somewhere in between the two earlier works. It contains passages of equally dense and unusual sonorities to Nuits while contrasting these with simpler, more harmonious sections. One of the most striking elements of this piece is the fixed mode resembling the pentatonic scale used in Javanese gamelan music. The melodies gain a certain ethnic resonance and harmonic color because of this technique. This new aspect of Xenakis's music was quite a surprise to many listeners, but remained an important element in a whole series of works right through the 1980s. Serment does not attempt to portray the Hippocratic Oath in detail, but it does set the words to a richly evocative music that evokes ancient times and distant cultures along with modern sensibilities and tensions.