Context :

Aims : Large abundance anomalies have been previously detected in Horizontal Branch B-type stars .
It has been suggested that at T _ { eff } > 11 000 K the stellar atmospheres become susceptible to diffusion effects and thus develop surface abundances similar to those that appear in main-sequence chemically peculiar group of A and B-type stars .
We present the first high resolution study of isotopic anomalies and chemical abundances in six Horizontal Branch B-type stars in globular clusters NGC 6397 and NGC 6752 and compare them to those observed in HgMn stars .

Methods : We obtained high-resolution ( up to R \sim 115 000 ) UVES spectra of a representative sample of six B-type stars ( T183 , T191 , T193 , B652 , B2151 , B2206 ) with sharp spectral lines ( v sin i \leq 10 km s ^ { -1 } ) .
The stars , T183 and B2151 , were observed on two consecutive nights to examine potential spectrum variability .
A detailed spectrum analysis is done relying on Kurucz ATLAS9 and ATLAS12 models .
The spectra are analysed using the SYNTHE code to generate synthetic spectra .

Results : It is the first time an abundance analysis is performed for all elements for which spectral lines were detected in UVES spectra of Horizontal Branch B-type stars .
Our study of these stars revealed no signs of He isotopic anomalies which would produce a ^ { 3 } He/ ^ { 4 } He ratio different from the solar one .
The isotopic anomaly of Ca is detected in all six studied stars .
The chemical abundance analysis reveals an overabundance over the solar values of P , Ti , Mn , Fe , and Y and an overabundance over the cluster metallicity of Mg , Ca , and Cr .
This behaviour is very similar in all six studied stars of both clusters with a few exceptions : The Na abundance is by more than 1.4 dex larger than the cluster metallicity in B652 , and by more than 0.8 dex larger than the cluster metallicity in B2206 ; the Co abundance is 1.0 dex over the solar abundance for T191 , while Zr is overabundant over the solar abundance by 0.4 dex in B2206 .
No lines of Hg or other heavy elements were observed in the spectra .
Weak emission lines of Ti ii , similar to those frequently observed in HgMn stars were discovered in one Horizontal Branch B-type star T191 .
Further , we detected a radial velocity change of 0.9 km s ^ { -1 } from one night to the next for T183 and 0.4 km s ^ { -1 } for B2151 .
Further high-resolution observations are necessary to examine whether both stars are spectroscopic binaries .

Conclusions :