Background Rifampicin lowers nevirapine plasma concentrations by inducing cytochrome P450. However, few data are available on this interaction during the lead-in period of nevirapine treatment. Methods Eighteen HIV-1/tuberculosis co-infected adults receiving rifampicin daily as part of anti-tuberculosis therapy were evenly randomized to nevirapine initiation by dose escalation (NVP200) or nevirapine initiation at 200 mg twice daily (NVP400). Subjects underwent 12 h intensive pharmacokinetic sampling on Days 7, 14 and 21 of nevirapine treatment. A minimum effective concentration (MEC) of 3000 ng/mL was used to interpret nevirapine concentrations 12 h after dosing (C(12)). Trial registration number: NCT00617643 (www.clinicaltrials.gov). Results Day 7 geometric mean nevirapine C(12) [90% confidence interval (CI)] was 1504 (1127-2115) ng/mL and 3148 (2451-4687) ng/mL in the NVP200 and NVP400 arms, respectively (P < 0.01). Nevirapine C(12) on Days 14 and 21 was similar. On Day 21, nevirapine concentration in 64% of patients was below the MEC. On Day 7, geometric mean area under the curve (AUC(0-12)) was lower in the NVP200 arm, 25 223 (90% CI, 21 978-29 695) ng.h/mL versus 43 195 (35 607-57 035) ng.h/mL in the NVP400 arm (P < 0.01). Similarly, on Day 14, nevirapine AUC(0-12) was lower in the NVP200 arm 23 668 (18 253-32 218) ng.h/mL versus the NVP400 arm 44 918 (36 264-62 769) ng.h/mL (P = 0.03). Conclusions In co-treated patients, nevirapine concentrations were below the MEC during initiation with dose escalation. Nevirapine initiation at the maintenance dose of 200 mg twice daily is preferred. Sub-therapeutic nevirapine concentrations were common at Day 21 with either regimen. Evaluation of higher nevirapine maintenance doses may be considered.