In 25 consecutive cases of chromium contact allergy we have made four parallel serial dilution tests and irradiated three of the test rows, two with solar-spectriim-like radiation from a 150 W Xenon lamp (4/5 MED and 4 MED) and one row with long-wave ultraviolet radiation (blacklight) alone.

Comparing an unirradiated row (control) and the row irradiated with 4/5 MED, the reactions were significantly more intense in 48% of the cases, i.e. the patients reacted at lower chromium concentrations.

In a corresponding comparison with 4 MED a significantly more intense reaction was obtained in 36% of the cases, whereas blacklight showed no significant difference compared with the control row.

The most intense reactions were obtained in the cases which were anamnestically photosensitive and had low MED values.