We examined potential predictors of therapists' "Stressful Involvement" (SI) among variables reflecting the psychotherapy process, therapist characteristics, patients' symptom severity or context variables (treatment setting). Ninety-eight sequences from individual psychodynamic treatments conducted by 26 therapists were studied. Data were analyzed using mixed regression models. Between-therapist and within-therapist variance accounted for most of the difference in SI. SI was strongly associated with negative feelings of the therapist about patient and therapy in the time between sessions. Therapists with more 'unassertive' and 'vindictive' interpersonal styles were also more prone to experiencing SI. The strong association of SI with therapist rather than patient characteristics and process ratings indicates the importance of further study of the therapist as a person and participant in psychotherapy.