We measured pH in situ in the top organic soil horizons in heathland and pine forest and found values between 2.6 and 3.2. This was 0.5e0.8 units lower than concurrent laboratory pH measurements of the same soil, which raises questions about the interpretation of pH measurements. We propose that the higher pH recorded by standard laboratory methods may be due to buffering ions from soil biota released from drying, grinding and rewetting of soil samples, whereas the in situ pH reflects the correct level of acidification