Contemporary microtonal music poses considerable challenges to professional performers. Here, we investigate five renditions of Klaus Huber’s "...Plainte..." for viola d’amore in third-tone tuning with respect to pitch accuracy at the acoustic level. The analysis also includes examining tones on open strings, which were played on the composer’s instrument. Significant differences between intended and realized fundamental frequency values were observed. The tuning of instruments deviated 14 to 42.5 cents from theoretical values. Influences of sound production on fundamental frequencies in performances were analysed, supplemented by additional analyses using the composer’s instrument. In each performance, the range of fundamental frequency deviations of tones played on open strings was considerably narrower than when tones were played with fingerboard stopping. In latter case, the range of deviations exceeded a third-tone interval (67 cents) in all performances and was larger than reported on tonal music in twelve-tone equal temperament. These results suggest specific limitations in the realization of third-tone music as performed on a fretless string instrument by highly-trained professional performers. The fact that three of the analysed recordings are commercially available further suggests that rather large deviations of fundamental frequencies from values described by music theory are accepted aesthetically.