The gravitationally lensed quasar B1600+434 ( z = 1.61 , m _ { V } = 21.6 ) has been observed at the 2.56m Nordic Optical Telescope ( NOT ) .
In this Letter we report the discovery of an edge-on late-type galaxy located between the two lensed components ( separation 1 \farcs 4 ) , close to the fainter image .
The galaxy photometry indicates that its redshift is approximately 0.4 .
We detect a large colour difference between the two images due to significant obscuration of the faint image .
The estimated amount of absorption as a function of colour indicates that the extinction may be due to dust in the lensing galaxy .
We also present evidence of flux variability in B1600+434 with a detected change of \sim 0.25 mag in one year .
The theoretically expected time delay is of the order of one month and so the system may be an interesting object for determining the Hubble constant .