Background Internet-administered cognitive behavioural therapy (iCBT) is an effective treatment of depression, yet much remains to be learned about the specific mechanisms influencing symptom reduction. Although previous research has consistently shown that therapist-guided iCBT is more effective than unguided iCBT, it is unknown whether the medium used for therapist-client communication has an impact on results. Methods Thirty-eight subjects with major depression were recruited from the waiting list of another iCBT study and randomised to a guided iCBT program with therapist guidance either by telephone calls (n =19) or e-mail correspondence (n =19). Outcome measures were self-rated measures of depression, anxiety and quality of life. Results At post-treatment, both groups showed significant and large symptom reductions yet did not differ from each other. Neither was there any between-group difference in client-rated therapeutic alliance or treatment engagement. Symptom reductions were maintained at a three-month follow-up. Conclusion Therapist guidance by telephone does not appear to differ from therapist guidance by e-mail in iCBT for depression, although further research featuring larger samples is necessary to draw more definite conclusions. Trial registration: None 
The impact of telephone versus e-mail therapist guidance on treatment outcomes, therapeutic alliance and treatment engagement in Internet-delivered CBT for depression: A randomised pilot trial