Sixty-five inpatients of a psychosomatic hospital in the Federal Republic of Germany with the diagnosis of anxiety neurosis (n = 31) or neurotic depression (n = 34) as defined by the International Classification of Disease (ICD-9), were randomized to a 4-week course of ipsapirone at 7.5 mg t.i.d. or placebo in a prospective, double-blind clinical trial to assess safety, tolerability, and efficacy. This article reports the efficacy results for those patients with the diagnosis of neurotic depression. The primary efficacy variable for patients with neurotic depression was the change from baseline in the Hamilton Rating Scale for Depression (HAM-D) at 4 weeks of treatment. Considering all of the randomized patients with neurotic depression (n = 34, the intent-to-treat population), the mean change from baseline in the HAM-D at Week 4 (observed cases) was -13.13 +/- 6.06 (n = 16) for the ipsapirone group, and -3.19 +/- 5.99 (n = 16) for the placebo group (p less than .001). A parallel analysis of the change from baseline in the Core Depression score of the HAM-D (defined as the sum of items 1, 2, 3, 7, and 8) also showed a significant treatment difference (p less than .01). Results were similar for the intent-to-treat population, last observation carried forward. Safety and tolerability were evaluated for all study patients independent of diagnosis. Treatment-emergent events (n = 65) were reported by 76 percent of patients treated with ipsapirone (n = 33) and by 38 percent of patients treated with placebo (n = 32).(ABSTRACT TRUNCATED AT 250 WORDS)