The appearance of this article was prompted by the discovery of a new block of inscriptions from the island of Kos, published in the 50th volume of the journal Chiron by D. Bosnakis and K. Hallof. Among these inscriptions, dating to 243 BC, of particular interest are two royal letters concerning the recognition of the right of asylum possessed by the temple of Asclepius in Kos. The first letter belongs to the king of Bithynia Ziaelas, and the second – to the Seleucid queen Laodice I, the mother of Seleucus II and Antiochus Hierax. Analysis of the contents of these documents compels us to rethink the commonly held assumptions about the foreign policy orientation of King Ziaelas from the second half of the 240s BC. Based on the already known earlier letter of Ziaelas to the citizens of Kos (IGXII, 4, 1, 209), together with the evidence of the Chronicle of Eusebius of Caesarea (Euseb. Chron. Schoene, I, 251), many researchers believe in the existence of a long-term alliance between this Bithynian king and Ptolemy III Everget, formed at the beginning of the second half of the 240s BC and lasting at least until the mid-230s BC. Instead, given the observations made on the basis of the new royal letters by D. Bosnakis, K. Hallof, and the author of this article, we can speak of only a very shortlived political partnership between Ziaelas and Ptolemy III. Afterwards, Ziaelas quickly returned to the Seleucid political orbit. This conclusion follows from the absence of references to Ptolemy III in the new letter of the Bithynian king, combined with indications of contacts between the latter and Laodice I, openly hostile to Everget. This move by Ziaelas was probably dictated by the lack of tangible military or political support from the Alexandrian ruler. The fact of the rupture of the short-lived relationship between Ziaelas and Ptolemy III, together with the testimony of the already known sources, suggests that the king of Bithynia continued permanently in the Seleucid sphere of influence.