An injector apparatus (10; 110) for use with a container (20; 120) of therapeutic material to deliver a metered dose of therapeutic material therefrom, the apparatus comprising: a first body (30; 130) fixed in use to the container and defining a first conduit portion (32;132) for the delivery of the therapeutic material from said container; a second body (40; 140) slidably connected to the first body (30; 130) and defining a second conduit portion (42; 142), in fluid communication with the first conduit portion, and wherein the second body (40; 140) is provided with or arranged to receive a delivery needle (44; 144) at the forward end of the injector apparatus through which a conduit (32,42; 132,142) defined by the first conduit portion (32; 132) and the second conduit portion (42; 142) is arranged to deliver therapeutic material in use; the injector further comprising a first non-return valve (70a; 170a) to prevent flow from the conduit (32, 42; 132, 142) to the container (20; 120) and a second non-return valve (70b; 170b) to prevent flow from the needle (44; 144) to the conduit (32, 42; 132, 142); wherein relative sliding motion between the first body (40; 140) and second body (30; 130) results in the displacement of one of the conduit portions (32, 42; 132, 142) into the other conduit portion (42, 32; 142, 132) such that the volume of the conduit may be decreased; characterised in that the injector apparatus further comprises: a biasing means (50; 150) provided such that the first (30; 130) and second (40; 140) body are biased towards an extended position in which the volume of the conduit (32, 42; 132, 142) is maximised; a catch (36, 46) arranged to hold the first (30; 130) and second (40; 140) body in a retracted position against said bias, said catch (36, 46) comprising complementary interconnecting features on the first and second body;and a cap (80; 180), said cap being arranged to prevent release of the catch (36, 46) in a closed position. a first body (30; 130) fixed in use to the container and defining a first conduit portion (32;132) for the delivery of the therapeutic material from said container; a second body (40; 140) slidably connected to the first body (30; 130) and defining a second conduit portion (42; 142), in fluid communication with the first conduit portion, and wherein the second body (40; 140) is provided with or arranged to receive a delivery needle (44; 144) at the forward end of the injector apparatus through which a conduit (32,42; 132,142) defined by the first conduit portion (32; 132) and the second conduit portion (42; 142) is arranged to deliver therapeutic material in use; the injector further comprising a first non-return valve (70a; 170a) to prevent flow from the conduit (32, 42; 132, 142) to the container (20; 120) and a second non-return valve (70b; 170b) to prevent flow from the needle (44; 144) to the conduit (32, 42; 132, 142); wherein relative sliding motion between the first body (40; 140) and second body (30; 130) results in the displacement of one of the conduit portions (32, 42; 132, 142) into the other conduit portion (42, 32; 142, 132) such that the volume of the conduit may be decreased; characterised in that the injector apparatus further comprises: a biasing means (50; 150) provided such that the first (30; 130) and second (40; 140) body are biased towards an extended position in which the volume of the conduit (32, 42; 132, 142) is maximised; a catch (36, 46) arranged to hold the first (30; 130) and second (40; 140) body in a retracted position against said bias, said catch (36, 46) comprising complementary interconnecting features on the first and second body;and a cap (80; 180), said cap being arranged to prevent release of the catch (36, 46) in a closed position. a biasing means (50; 150) provided such that the first (30; 130) and second (40; 140) body are biased towards an extended position in which the volume of the conduit (32, 42; 132, 142) is maximised; a catch (36, 46) arranged to hold the first (30; 130) and second (40; 140) body in a retracted position against said bias, said catch (36, 46) comprising complementary interconnecting features on the first and second body;and a cap (80; 180), said cap being arranged to prevent release of the catch (36, 46) in a closed position.