The clinical efficacy and safety of deproteinized hemodialysate from calf blood (Actovegin) was tested in the treatment of Achilles paratendinitis in a double-blind, placebo-controlled, monocentric study. Both study groups (with 30 patients each) were homogeneous at the beginning of the study with respect to the study variables. Each patient received three injections into the paratendinous sliding tissue at intervals of 3–5 days. The results showed a highly significant difference between the two study groups with respect to the primary variable “Achilles tendon diameter.” With regard to stress from full athletic activity, the subjective symptoms improved significantly faster with drug therapy compared with placebo treatment. Pain reduction in the drug group was likewise significantly higher than that observed in the placebo group. Correlating to the clinical results, the patients' assessment of therapeutic success also demonstrated significant superiority of the drug group. No adverse drug effects were observed in the framework of the present study.