We present the first results of an observational project , which addresses the period changing behaviour of a sample of high-amplitude \delta Scuti stars .
In this paper we discuss the double-mode nature of V567 Ophiuchi .
It was observed on 15 nights in two consecutive years in order to resolve the long-standing ambiguity related to its secondary period .
A frequency analysis of almost 5000 individual single-filtered CCD V measurements resulted in two independent frequencies ( f _ { 1 } = 6.6879 d ^ { -1 } and f _ { 2 } = 11.8266 d ^ { -1 } ) with a ratio of f _ { 1 } / f _ { 2 } = 0.565 .
Earlier data taken from the literature were used to refine the dominant period , and the re-analysis supports the existence of the secondary period .
Possible asteroseismological implications are briefly discussed .