A number of papers have tested for rational bubbles in the post-World War I hyperinflation in Germany. The present paper henceforth FHS does so in Poland around the time of the ‘big bang’. It finds some evidence that ‘the main determination of the hyperinflation was a rational bubble’ but cautiously notes that conventional structural models might also explain the hyperinflation. I salute their technically sophisticated investigation of this interesting question, but in the end find their evidence distinctly less suggestive of bubbles than do they. This evidence comes from a nice extension of techniques suggested by Diba and Grossman (1984) and Hamilton and Whiteman (1985), and applied to the German hyperinflation by Hamilton and Whiteman (1985). Using the Cagan model, that paper noted that in the absence of bubbles, prices will have the same order of integration as does money; if money is, say, Z(2) so that what is stationary is changes in the growth rate of money but not the growth rates themselves then prices should be Z(2) as well. But bubbles cause explosive growth, so no level of differencing will induce stationarity in a variable driven wholly or even in part by a bubble. Hamilton and Whiteman (1985) found that prices and money appeared to be Z(2) in the German hyperinflation, and concluded that bubbles probably were not present. Evans (1991) in turn pointed out that if (a) bubbles periodically grow and collapse, and (b) there are not a whole lot of observations during which the bubble was growing, the Hamilton and Whiteman (1985) test will likely fail to find bubbles. And tests are likely to find that prices and money are