Previous studies (Barcroft & Sommers, 2005; Sommers & Barcroft, 2007) have demonstrated that variability in talker, speaking style, and speaking rate positively affect second language vocabulary learning, whereas variability in overall amplitude and fundamental frequency (F0) do not, at least for native English speakers. Sommers and Barcroft (2007) hypothesized that English speakers do not benefit (with regard to second language vocabulary learning) from amplitude and F0 variability because these are not phonetically relevant to them. The present study further tested this hypothesis by examining effects of F0 variability among adults who speak a tone language (Zapotec-Spanish bilinguals) and those who do not speak a tone language (Spanish speakers with substantial knowledge of English). Participants attempted to learn 24 Russian words while hearing the words and viewing their corresponding pictures. Three levels of F0 variability were compared. Fundamental frequency variability significantly improved vocabulary learning for speakers of the tone language (Zapotec) but not for the Spanish speakers. This result provides strong evidence that effects of acoustic variability on learning new word forms depend on phonetic relevance.