Culp (1994) provides a defense for a form of experimental reasoning entitled ‘robustness’. Her strategy is to examine a recent episode in experimental microbiology—the case of the mistaken discovery of a bacterial organelle called a ‘mesosome’—with an eye to showing how experimenters effectively used robust experimental reasoning (or could have used robust reasoning) to refute the existence of the mesosome. My plan is to criticize Culp's assessment of the mesosome episode and to cast doubt on the epistemic significance of robustness. In turn, I present a different account of the experimental reasoning microbiologists used in arriving at the conclusion that mesosomes are artifacts. I call this form of reasoning ‘reliable process reasoning’, and close the paper with a brief discussion of how experimental microbiologists justify the claim that an experimental process is reliable.