Abstract: We report on the RXTE detection of a sudden increase in the absorption column density, NH, during the 2011 May outburst of GX 304-1. The NH increased up to ~16 × 10(exp 22) atoms cm(exp -2), which is a factor of 3–4 larger than what is usually measured during the outbursts of GX 304-1 as covered by RXTE. Additionally, an increase in the variability of the hardness ratio as calculated from the energy resolved RXTE-Proportional Counter Array light curves is measured during this time range. We i…