Abstract. In this study, we explore the correlation of I/Ca ratios in three calcitic and one aragonitic foraminiferal species. I/Ca ratios are evaluated as possible proxies for changes in ambient redox conditions across the Peruvian oxygen minimum zone to the ambient oxygen concentrations in the habitat of the foraminiferal species studied. Cleaning and measurement methods for the determination of I/Ca ratios are tested. All species show a positive trend in their I/Ca ratios as a function of higher oxygen concentrations. The most promising species appears to be Uvigerina striata, which shows a highly statistically significant correlation between I/Ca ratios and bottom water (BW) oxygenation (I/Ca = 0.032(±0.004) × [O₂]_BW + 0.29(±0.03), R² = 0.61, F = 75, P < 0.0001). Only for the aragonitic species Hoeglundina elegans is this relationship not significant. The iodine volatility in acidic solutions, the species dependency of I/Ca–[O₂]_BW correlations, and the individual variability of single tests, need to be accounted for when applying the I/Ca ratio as a proxy for redox conditions.