Speech fundamental frequencies (SFFs) are nonverbal sound frequencies that convey emotion in speech. The degree of SFF long-term averaged spectra (LTAS) convergence between conversants reflects aspects of conversant-reported quality of the interaction (e.g., emotional synchrony). This study investigated whether SFF LTAS convergence between inpatients diagnosed with schizophrenia (n = 20) and an interviewer was associated with severity of illness (SOI), formal speech disturbance (FSD), and stress reactivity of FSD. Participants provided speech samples describing stressful and nonstressful life experiences. In the stress condition, SFF LTAS was negatively correlated with SOI and FSD. Moreover, patients exhibiting stress reactivity of FSD also evidenced stress reactivity of SFF LTAS. These findings suggest that the emotional and verbal contents of speech are disrupted by stress in schizophrenia, and SOI is associated with FSD and reduced emotional communication during stressful conditions. The interaction between stress reactivity of FSD and SFF LTAS supports the construct validity of a reactivity dimension in schizophrenia.