  Most of the current theories suggest the lambda Bootis phenomenon to
originate from an interaction between the stellar surface and its local
environment. In this paper, we compare the abundance pattern of the lambda
Bootis stars to that of the interstellar medium and find larger deficiencies
for Mg, Si, Mn and Zn than in the interstellar medium. A comparison with metal
poor post-AGB stars showing evidence for circumstellar material indicates a
similar physical process possibly being at work for some of the lambda Bootis
stars, but not for all of them. Despite the fact that the number of
spectroscopically analysed lambda Bootis stars has considerably increased in
the past, a test of predicted effects with observations shows current abundance
and temperature data to be still controversial.
