Paclitaxel (Taxol), a new antineoplastic drug, has been reported to be neurotoxic at doses above 200 mg/m2 per course. It is uncertain whether neurotoxicity is related to cumulative amounts of paclitaxel. Neuropathy was prospectively assessed in 18 patients with breast cancer, receiving between two and eight courses of 135 or 175 mg/m2 of paclitaxel. Vibratory perception thresholds (VPT) and tendon reflex scores were proportionally related to the corresponding cumulative amounts of paclitaxel (P = 0.002; P = 0.0003). The amounts of paclitaxel administered between the first and last assessments (175-1225 mg/m2) were related to concomitant changes in VPT (P = 0.034). Paclitaxel had no clear neurotoxic threshold; if present, it lies below 540 mg/m2. Rather, VPT appeared to increase 0.1 micron per 400 mg/m2 over the entire range of 175-1225 mg/m2 of paclitaxel. Clinical neuropathy prevailed in 0/8 patients at screening and in 5/10 patients at the final assessment (P = 0.029). Neuropathy never exceeded grade 1. Thus, although neurotoxicity of paclitaxel is frequent and cumulative, it remains mild or subclinical up to at least 1400 mg/m2 administered over eight cycles.