Natural circulating antibodies (NAbs) to endogenous regulators have shown to be potential biomarkers in medicine. Due to the lack of reliable assays, only few of them have been well studied. To employ NAbs as biomarkers, an evaluation of changes over the course of a treatment is required. This paper describes our work to analyze the dynamics of NAbs titer to interferon-gamma (IFN-γ) among healthy children of different age and in patients with varicella infection receiving an antiviral drug Anaferon for children (AC, the API are highly diluted antibodies to IFN-γ) in comparison with placebo, and to correlate the findings with the treatment results. IFN-γ plays an essential role during varicella infection, and this fact causes the consequent increase of NAbs to IFN-γ level. The mean anti-IFN-γ NAbs level in the healthy volunteer group was 101 × 103 U/ml (age: 0–15 years), which was significantly lower than the mean pre-treatment value in patients with varicella infection 167 × 103 U/ml (age: 3–17 years). In the AC group, the NAbs level observed on days 5 and 10 decreased significantly to a level of 154 × 103 U/ml, whereas in the placebo group it continued to rise in a time-dependent manner reaching 229 × 103 U/ml on day 10. Our findings suggest that treatment with AC is characterized by “normalization” of the anti-IFN-γ NAbs levels in patients with varicella infection.