Objective - To study the reliability of a proving methodology and the reproducibility of proving symptoms.Methods - Two homeopathic medicines and placebo were given, in a double-blind randomized design, to 31 healthy volunteers (13 Piper methysticum 30C, 11 placebo and 7 Plumbum metallicum 30C), 5 drops 4 times daily, until the onset of unbearable symptoms, or at most for 1 week. The primary outcome measure was the number of phrases containing unusual or new symptoms selected by supervisors (SEL) from unstructured diaries and the number of these symptoms (SYM) present in SELs. The secondary outcome measures were the number of symptoms with modalities of both verum groups concordant with symptoms reported in a previous proving of Plumbum 12C. Other parameters evaluated were repeated and crossed symptoms in SELs.Results - Both medicines showed qualitative and quantitative differences from placebo. Piper: 146 SELs (median: 5), Plumbum: 118 SELs (16), placebo: 48 SELs (2), containing 260 (8), 199 (29) and 58 (2) SYMs, respectively. There was a significant difference from placebo in Plumbum but not in Piper SELs and SYMs (P<0.05). 31, 24 and 4 ‘repeated’ and 18, 22 and 2 ‘crossed’ symptoms were found in Piper, Plumbum and placebo. 8 and 30 symptoms concordant with the classical proving of Plumbum were found for Piper and Plumbum, corresponding to about 10% and 45% of their total SELs.Conclusions - Open diaries, supervision and double-blind placebo are useful methods in homeopathic pathogenetic trials. Estimates of concordance should be introduced in proving methodology.