Thirty adults undergoing elective upper limb surgery received an US-guided retrograde infraclavicular block. The initial concentration of 0.5% ropivacaine injected was 30 ml, which was subsequently varied at a ratio of 1: 1.2 for each consecutive patient according to the response of the previous patient. The medium effective volume (EV50) was determined using the Dixon and Massey up-and-down method. The effective volume in 95% of patients (EV95) was calculated using probit regression.