diff --git a/t/plot00_pgplot.t b/t/plot00_pgplot.t
index c5fd7bc..559c5cc 100644
--- a/t/plot00_pgplot.t
+++ b/t/plot00_pgplot.t
@@ -4,6 +4,11 @@ use strict;
 use Test::More;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
+
  # pgbegin( $unit, $file, $nxsub, $nysub );
  eval { require PGPLOT; PGPLOT::pgbegin(0,"/xw",1,1) };
  if ( $@ ) {
diff --git a/t/plot00_plplot.t b/t/plot00_plplot.t
index 63dd8b2..9e068ff 100644
--- a/t/plot00_plplot.t
+++ b/t/plot00_plplot.t
@@ -4,6 +4,11 @@ use strict;
 use Test::More;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
+
  eval {require Graphics::PLplot; };
  if ( $@ ) {
    plan skip_all => "Graphics::PLplot module not installed.";
diff --git a/t/plot00_tk.t b/t/plot00_tk.t
index d96000f..cb2409a 100644
--- a/t/plot00_tk.t
+++ b/t/plot00_tk.t
@@ -4,6 +4,10 @@ use strict;
 use Test::More;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
 
  eval "use Tk; use Tk::Button;";
  if ( $@ ) {
diff --git a/t/plot00_tk_zinc.t b/t/plot00_tk_zinc.t
index 61bff0d..49511c3 100644
--- a/t/plot00_tk_zinc.t
+++ b/t/plot00_tk_zinc.t
@@ -4,6 +4,10 @@ use strict;
 use Test::More;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
 
  eval "use Tk; use Tk::Button;";
  if ( $@ ) {
diff --git a/t/plot_pg.t b/t/plot_pg.t
index a28cc35..f39000b 100644
--- a/t/plot_pg.t
+++ b/t/plot_pg.t
@@ -10,6 +10,10 @@ require_ok( "Starlink::AST::PGPLOT" );
 use File::Spec;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
 
  eval { require PGPLOT; PGPLOT::pgbegin(0,"/xw",1,1) };
  if ( $@ ) {
diff --git a/t/plot_pl.t b/t/plot_pl.t
index 180ec31..0f472c2 100644
--- a/t/plot_pl.t
+++ b/t/plot_pl.t
@@ -10,6 +10,10 @@ require_ok( "Starlink::AST::PLplot" );
 use File::Spec;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
 
  eval "use Graphics::PLplot";
  if ( $@ ) {
diff --git a/t/plot_tk.t b/t/plot_tk.t
index 59b3f30..ca8008b 100644
--- a/t/plot_tk.t
+++ b/t/plot_tk.t
@@ -5,6 +5,10 @@ use Test::More;
 use Data::Dumper;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
 
  eval "use Tk; use Tk::Button";
  if ( $@ ) {
diff --git a/t/plot_tk_zinc.t b/t/plot_tk_zinc.t
index e5ed7c5..9db82e7 100644
--- a/t/plot_tk_zinc.t
+++ b/t/plot_tk_zinc.t
@@ -6,6 +6,10 @@ use Data::Dumper;
 use File::Spec;
 
 BEGIN {
+ unless (exists $ENV{'DISPLAY'}) {
+   plan skip_all => '$DISPLAY is not set.';
+   exit;
+ }
 
  eval "use Tk";
  if ($@) {